A Demand System Analysis of Organic and Conventional Fresh Milk in Germany Segmented by Consumer Groups*

Transcription

1 A Demand System Analyss of Organc and Conventonal Fresh Mlk n Germany Segmented by Consumer Groups* Rebecca Schröck Insttute of Agrcultural Polces and Market Research Justus-Lebg-Unversty of Gessen, Senckenbergstr. 3, Geßen Emal: rebecca.schroeck@ernaehrung.un-gessen.de Paper prepared for presentaton at the EAAE 2011 Congress Change and Uncertanty Challenges for Agrculture, Food and Natural Resources August 30 to September 2, 2011 ETH Zurch, Zurch, Swtzerland * The artcle was wrtten n the framework of a research project whch s funded by the German Federal Mnstry of Educaton and Research (BMAS). The project fundng reference number s 2808OE148. The author takes full responsblty for the contents of ths paper. Specal thanks go to the staff members of the Department of Agrcultural and Food Marketng at the Unversty of Kassel under the drecton of Prof. Dr. Ulrch Hamm. They prepared the data for ths research project and provded them to the Insttute of Agrcultural Polces and Market Research at the Unversty of Gessen for further research. Copyrght 2011 by [SCHRÖCK]. All rghts reserved. Readers may make verbatm copes of ths document for non-commercal purposes by any means, provded that ths copyrght notce appears on all such copes.

2 A Demand System Analyss of Organc and Conventonal Fresh Mlk n Germany Segmented by Consumer Groups 1 Introducton In Germany as well as n most ndustralzed countres the market for organc food has grown rapdly wthn the last few years. In 2009, organc food sales n Germany added up to 5.8 bn., representng 3.4 % of total food sales (BÖLW 2010). Organc mlk, n partcular, accounted for 14 % of retal fresh mlk sales, underlnng that mlk plays an mportant role n the organc food market (BÖLW 2009). However, organc mlk sales are dstrbuted qute heterogeneously between consumer groups: The commtted buyers of organc mlk account for just 5 % of total mlk expendtures but for more than 87 % of total organc mlk expendtures. Except for fresh produce, organc mlk was one of the frst organc products avalable to a consderable share of consumers (DEMERITT 2004). In ts early stage of ntroducton, n Germany as well as n the U.S., brand products led the way, whch were manly sold by drect sales or n specalty stores (DIMITRI & VENEZIA 2007). Snce then, the compettve structure of the organc mlk market and the range of products offered have changed dramatcally. Dscounters and supermarkets have entered the market. Ths development has been attended by the appearance and expanson of organc prvate labels. Currently, nearly every dscounter and supermarket offers both organc and conventonal mlk. Qute often consumers have wde choces between brand products and those of prvate-labels. Thus, the organc mlk market n Germany now seems to be well-establshed. The typcal fndng of studes that nvestgate consumer responsveness wth respect to organc mlk prcng s that the demand for organc mlk s much more elastc than the demand for conventonal mlk (see e.g., GLASER & THOMPSON 2000; DHAR & FOLTZ 2005; JONAS & ROOSEN 2008; ALVIOLA & CAPPS 2010). However, these studes were manly conducted n earler stages of the organc mlk market. As a result of the structural changes descrbed above, t s questonable whether pror studes can account approprately for the current market analyss. Gven ths background, the objectve of ths study s to update and to extend the analyss of household demand for organc and conventonal mlk n Germany. Combnng actual purchase and demographc data and applyng a two-step demand system approach, the study dentfes and quantfes the factors determnng the demand for organc and conventonal fresh mlk. Ths paper contrbutes to the body of lterature by provdng estmates of prce and expendture elastctes not only for the whole populaton but also for several consumer groups whose respectve populaton shares wll probably change n future. Estmatng demand elastctes at a dsaggregated level wth smultaneous consderaton of structural and demographc trends allows for predctng future demand more accurately. The artcle s organzed as follows: Secton 2 surveys the htherto exstng lterature on the demand for organc mlk. In secton 3, the conceptual model s presented. Secton 4 ntroduces the data, the GfK Homescan Panel. Secton 5 covers the econometrc evdence and provdes nterpretatons of the results. Fnally, conclusons are presented n secton 6. 2 Lterature revew There are two strands of organc food research that are closely lnked to the present paper. The frst one examnes the organc consumer profle wth respect to socodemographc characterstcs, as well as atttudes and cultural norms. The second one analyzes consumer purchasng behavour especally ther responsveness to changes n prces and ncome. Scentfc answers to the queston Who s the organc food consumer? are really multfaceted and sometmes contradctory. Studes conducted n the U.S. often suggest that organc consumers are female, marred, wealthy, whte and well-educated (e.g., BUZBY & SKEES 1

3 1994; THOMPSON 1998; GOVINDASAMY & ITALIA 1999; HUGHNER et al. 2007; SMITH, HUANG & LIN 2009; DETTMANN & DIMITRI 2010). However, results are not unform, nether wth respect to socoeconomc nor to demographc characterstcs. In fact, fndngs regardng consumer profle and behavour seem to depend strongly on perod, regon and methods of the study as well as on the commodty group and the sample 1. Therefore, further research should specfy these nfluencng factors and quantfy ther mpact. Relatng to the second strand of organc food research, Table 1 revews analyses that quantfy organc mlk consumer behavour. It shows country, sample perod and estmaton methods together wth a short classfcaton of the data base. GLASER and THOMPSON (2000) analyze the demand for organc and conventonal mlk n the U.S. usng monthly food retalng scanner data. Whle conventonal mlk s dfferentated nto brand and prvate-label mlk, the study does not dstngush between any subcategores for organc mlk. Applyng a Lnear Approxmated Almost Ideal Demand System (LA/AIDS), the authors fnd prce elastctes for conventonal prvate-label and conventonal brand mlk of and -0.73, respectvely. Accordng to ther results, demand for organc mlk s hghly prce-elastc (-3.64). Snce the organc mlk prce s generally hgher than the brand and the prvate-label mlk prces, the authors conclude that the hgher the prce level of the mlk product s, the more elastcally consumers react (GLASER & THOMPSON 2000, 13). Prce elastctes for conventonal mlk estmated by JONAS and ROOSEN (2008) show a smlar magntude: for conventonal prvate-label and for conventonal brand mlk. For organc mlk the authors fnd an even more elastc demand than GLASER and THOMPSON ( ). Ths result ndcates that organc mlk consumers are hghly prce senstve and that food retalers consequently face a very constraned prce settng potental. Table 1. Revew of studes analyzng the demand for organc mlk Authors Country Sample perod Data GLASER & THOMPSON (2000) DHAR & FOLTZ (2005) JONAS & ROOSEN (2008) MONIER et al. (2009) ALVIOLA & CAPPS (2010) CHOI & WOHLGENANT (2010) Source: Own complaton. U.S U.S AC Nelsen and IRI retal scanner data IRI retal scanner data for 12 U.S. ctes Estmaton method AIDS Q-AIDS Germany GfK Homescan Panel LA/AIDS France 2005 French TNS Worldpanel, Homescan data U.S Nelsen Homescan Panel data LA/AIDS Heckman twostep procedure U.S. 2004/ 2005 Nelsen Homescan Panel data LA/AIDS DHAR and FOLTZ (2005) who apply a quadratc AIDS (Q-AIDS) fnd own-prce elastctes for organc and conventonal mlk to be -1.4 and -1.0, respectvely. ALVIOLA and CAPPS (2010, 385) present own-prce elastcty estmates of for conventonal mlk and of -2.0 for organc mlk. Regardng the ncome elastcty they fnd organc mlk to be a necessty and conventonal mlk to be an nferor good. Hence, a consoldated vew of prevous studes ndcates that demand for organc mlk s much more elastc than demand for conventonal mlk. However, MONIER et al. (2009) and CHOI and WOHLGENANT (2010) arrve to conflctve conclusons. In contrast to the studes presented above, prce elastcty estmated by MONIER et al. 1 There are numerous studes nvestgatng the organc consumer profle usng varous methodologcal approaches. See, e.g., THOMPSON & KIDWELL (1998), BRUHN (2002), HILL & LYNCHEHAUN (2002), ZMP (2003), LI, ZEPEDA & GOULD (2007), ZEPEDA & LI (2007), JONAS & ROOSEN (2008), WIER et al. (2008), ZHANG et al. (2008), MONIER et al. (2009), PLAßMANN & HAMM (2009) and RIEFER & HAMM (2009). 2

4 (2009) s hgher for non-organc mlk (-1.02) than for organc mlk (-0.38). However, the prce elastcty for organc mlk s not sgnfcantly dfferent from zero. CHOI and WOHLGE- NANT (2010) analyze the U.S. mlk market at a dsaggregated level. They defne 20 mlk types by three dfferent characterstcs: fat content, flavour and organc clam. The results ndcate an elastc demand for both organc and conventonal mlk. The number of studes on the subject shows that there actually s emprcal evdence for dverse organc mlk markets. However, most studes are conducted n the U.S.. Econometrc analyses wth partcular emphass on the German market are scarce. Consderng that the sze and the structure of the U.S. organc mlk market dffers from that n Germany, t s lkely that consumer behavour and especally ther prce senstvty s not the same n both countres. 3 Methodologcal approach In lne wth prevous research, ths study apples a demand system,.e. the Almost Ideal Demand System (AIDS; see DEATON & MUELLBAUER 1980) to analyze the demand for organc and conventonal mlk. The demand for fresh mlk s assumed to be separable from the demand for other foods,.e. a two-stage budgetng approach s appled. Frst, the households decde on ther optmal expendtures on fresh mlk. Second, the households allocate the mlk expendture to the dfferent mlk types. It s postulated that households maxmze ther utlty functon subject to ther mlk budget x ht. Applyng an AIDS, the expendture share of household h on mlk type n perod t, w ht, can be expressed as follows: n * (1) w ht = + γ j log p jht + β log(xht /Pht ) + uht j= 1 α. n s the number of dfferent mlk products n the demand system, p j s the prce of the jth mlk type, u s an error term. P ht denotes the prce ndex. α, β, γ and u are the parameters to be estmated. To reduce the computatonal complexty we use the Lnear Approxmated AIDS (LA/AIDS) whch replaces the orgnal translog prce ndex by the lnear Stone Index: * (2) log Pht = w jt log p jht. n j= 1 w denotes the sample mean expendture share. Accordng to mcroeconomc theory, the LA/AIDS equaton defned n (1) has to fulfll the constrants of addng up ( α = 1, β = 1, γ j = 0 ), homogenety ( γ j = 0 ) and symmetry ( γ j = γ j ). In the followng the LA/AIDS model specfed n equaton (1) s refned n order to (a) ncorporate a set of socodemographc varables nto the demand system, (b) to account for dynamc changes n consumer behavour and (c) to deal wth the problem of censorng. Food choces, and especally the choce between organc and conventonal food are affected by socodemographc and economc factors (GOULD, COX & PERALI 1991, 213). It s assumed that socodemographc varables reflect taste and preferences whch, n turn, determne the consumpton of organc and conventonal mlk. The above LA/AIDS specfcaton can be modfed to ncorporate the mpact of socodemographc varables Z kht by usng the method of demographc translaton. Ths method preserves the lnearty of the demand system and allows demographc dfferences to shft both the ntercept and elastcty parameters (DHAR & FOLTZ 2005, 220). Under demographc translatng, the constant term n the budget share equaton (1), α, s composed of a constant α 0 and the mpact of socodemographc varables. Z kht denotes the k th socodemographc varable n household h and perod t, k=1,,k. Thus, the LA/AIDS s assumed to take the followng form: * (3) w ht = 0 + α k Z kht + γ j log p jht + β log( xht / Pht ) + uht k j α. j 3

5 n n The addng up restrcton requres that =1 α 0 = 1 and α k = 0. = 1 Analyzng a sample perod of fve years, the problem of temporally changes n consumer behavour arses. Recent shfts n the structure and the product assortment of the organc mlk market have certanly nfluenced consumer behavour. Presumably, general tendences that do not show any lnkage to prces and ncome such as technologcal progress (e.g. mplementaton of Extended-Shelf-Lfe mlk), ncreasng mportance of eatng away from home and an ncreasng awareness of healthy eatng contrbuted to the growth n the organc mlk demand. There are dfferent approaches when ncorporatng dynamc adjustment processes n demand systems. Thoroughly, more than one approach can be appled at the same tme (MOSCHINI & MORO 1996, 248). Frst, t s corrected for autocorrelaton and accounted for habt formaton by ncorporatng the dfferentated endogenous varable w ht (HANSEN 1993, 310). Consderng the fact that w ht s correlated wth the error term u, WICKENS and BREUSCH (1988, 189f) suggest to nclude the lagged consumpton w h,t-1 as an nstrumental varable nstead of usng w ht. Second, a trend s consdered n order to account for contnuously changng consumer behavour and structural changes over tme. Thus, equaton (3) s agan modfed: n 1 (4) w = ht + k Z kht + j p jht + xht Pht + * α 0 α γ β log( / ) σ j w jh, t 1 + δ trend + uht k j j log. In order to deal wth the problem of zero observatons, t s assumed that household s purchase decsons can be modeled as a two-step process. The applcaton of the two-step procedure developed by SHONKWILER and YEN (1999) allows for estmatng the demand system usng all observatons. Thus, households frst decde whether to buy a certan mlk type or not (partcpaton decson). If they decde to buy, they subsequently determne the quantty demanded (consumpton decson). Each of the household s decsons s determned by a dfferent set of explanatory varables. In the frst step, a multvarate probt regresson examnes whch determnants nfluence the purchase probablty. The probablty s then used as an nstrument to ncorporate the censorng latent varables n the second-step estmaton of the LA/AIDS (JONAS & ROOSEN 2008, 195). For each mlk type, the frst-step decson s modelled as a dchotomous choce problem. The dependent varable s Y ht =1 f household h purchased mlk type at least once n perod t, otherwse Y ht =0. (5) Y ht { user household = 1 } = X ht β + uht where u ht X ht ~ N(0,1). X ht s the vector of ndependent varables, β represents the correspondng coeffcents assocated wth X ht. In order to consder household-specfc heterogenety and habt formaton, the ndependent vector contans not only socodemographc varables but also past consumpton decsons,.e., the quantty demanded of the respectve mlk type n the prevous year. In demand theory, prces are crucal n determnng consumers food purchases. As organc mlk s lsted n more and more retal formats, t becomes avalable to a wder consumer base, whch s presumably less affluent and more prce senstve. Therefore, (organc) prce prema can be assumed to play an ncreasngly mportant role not only n the second-step but also n the frst-step decson (SMITH, HUANG & LIN 2009: 735). The prce prema are computed as the percentage above the average prce of conventonal prvate-label (CPL) mlk,.e. the mlk type wth the lowest prce, and also ncorporated as explanatory varables n the frst step: (6) prce premum p p ht CPL, t ht =. p CPL, t The consumpton partcpaton decson s hence modeled as a functon of socodemographc varables, past consumpton and prce prema. In a next step, the normal probablty densty functon pdf ( φ ht ), and the normal cumulatve dstrbuton functon cdf ( Φ ht ) were estmated 4

6 on the bass of the probt regresson results. These probablty functons enter the second-step demand system (specfed n equaton (4)) as latent varables correctng for censorng. Hence, the fnal specfcaton of the expendture share equaton s log. n 1 (7) * w ht = + k Z kht + j p jht + xht Pht + α 0 α γ β log( / ) σ j w jh, t 1 + δ trend Φ ht + λφht + uht k j j Equaton (7) s estmated as a demand system wth (n-1) equatons 2 va seemngly unrelated regressons. Prce and expendture elastctes are computed usng the formulas gven by GREEN and ALSTON (1990): (8) expendture elastcty: = + ˆ β ˆ η 1 w Φ ˆ ˆ γ β (9) uncompensated own- and cross prce elastcty: ε ˆ j w j ˆ = Φˆ j δ w δ denotes the Kronecker Delta and s δ=1 for j= and δ=0 for j. Fnally, the demand system was estmated separately for dfferent consumer groups. 4 Data and sample descrpton The analyss s based on the GfK Consumer Scan scanner panel dataset on food purchases of German households. Snce the begnnng of 2004 the GfK has put specal efforts to heghten the representatveness of the panel wth respect to organc food markets. Thus, the GfK data now has overcome ts prmary troubles wth the dstncton of organc and non-organc products. The GfK panel offers a perfectly qualfed dataset for ths knd of analyss n two aspects: Frst, food purchase nformaton s drectly lnked to socodemographc nformaton about the household. Second, reportng grocery purchases of 20,000 households 3 from a wde varety of retal outlets ncludng organc food shops and coverng a sample perod of fve years (January 2004 to December 2008) the panel provdes a really unque sample sze. Complng detaled nformaton for each mlk purchase lke date of purchase, amount bought, prce 4, brand chosen, name of the supermarket chan, fat content and organc clam, the dataset permts analyses at a qute dsaggregated level. Addtonally, the dataset ncludes socodemographc varables such as nformaton about age, educaton, professon and gender of the household head as well as characterstcs of the key household shopper. Moreover, the household s net ncome, household sze and number of kds are reported. In the followng, mlk wll be dstngushed nto prvate-label and brand mlk both for conventonal and organc mlk. Consequently, four dfferent mlk types are analyzed: organc brand (OB) mlk, organc prvate-label (OPL) mlk, conventonal brand (CB) mlk and conventonal prvate-label (CPL) mlk. 2 In dong so, the author follows SHONKWILER and YEN (1999). It was checked that the estmated coeffcents were stable regardless whch equaton was dropped. 3 The households n the GfK Homescan Panel comprse a stratfed random sample, selected on demographc as well as geographc targets. Stratfcaton ensures that the sample represents the socodemographc profle of consumers n Germany accordng to the German mcrocensus. 4 Panelsts of the GfK Consumer Scan do not report exact prces but total quantty and expendtures for each food tem they bought. Prces are computed as the unt value prce for each purchase by dvdng the reported expendtures by the correspondng quantty. These unt values may also reflect qualty dfferences and, consequently, the estmated elastctes may be based. However, the author consders the commodtes nvolved n ths analyss to be suffcently dsaggregated and homogeneous to mnmze the degree of bas (see COX & WOHLGENANT 1986). A second problem related to unt values s that they do not take effects of prce promotons nto account. However, for mlk ths should not cause serous bas, because mlk s rarely set on specal offer n Germany (LZ 2005). A thrd problem s that prces can only be constructed from reported purchases. Prces faced by non-users reman unobserved. Therefore, mssng prces are replaced through regonal averages calculated on data for consumng households (cf. JONAS & ROOSEN 2008, 197). 5

7 Table 2. Sample means of mlk expendtures and household characterstcs by consumer groups n Germany, Varable Whole sample Non-Buyers Occasonal Commtted Buyers Buyers M SD M SD M SD M SD Mlk quanttes purchased (sample means n lters/year) OB mlk 1.26 (0.045) 0.01 (0.000) 2.04 (0.075) (0.952) OPL mlk 1.42 (0.044) 0.01 (0.001) 3.13 (0.086) (0.900) CB mlk (0.262) (0.281) (0.999) (0.685) CPL mlk (0.371) (0.402) (1.190) (0.831) Budget shares (sample means n % of total mlk expendture) OB mlk of total mlk expendtures 0.01 (0.000) 0.00 (0.000) 0.02 (0.001) 0.28 (0.006) OPL mlk of total mlk expendtures 0.02 (0.000) 0.00 (0.000) 0.04 (0.001) 0.31 (0.006) CB mlk of total mlk expendtures 0.35 (0.001) 0.35 (0.001) 0.42 (0.004) 0.22 (0.004) CPL mlk of total mlk expendtures 0.62 (0.001) 0.65 (0.001) 0.51 (0.004) 0.18 (0.004) Income a) (sample means n Euro/month) Weghted per-capta net ncome 1,323 (2.101) 1,306 (2.196) 1,428 (8.285) 1,531 (11.51) Prce prema (sample means, percentage above the average prce of CPL mlk ) OB 1.57 (0.064) 1.57 (0.062) 1.53 (0.390) 1.59 (0.476) OPL 1.51 (0.058) 1.51 (0.057) 1.48 (0.332) 1.53 (0.357) CB 1.14 (0.093) 1.13 (0.095) 1.22 (0.384) 1.28 (0.550) Natonalty & Gender (% of the sample) German natonalty 0.94 (0.001) 0.92 (0.001) 0.93 (0.004) 0.93 (0.005) Female person 0.64 (0.002) 0.64 (0.002) 0.64 (0.007) 0.66 (0.009) Regon (% of sample) West 0.26 (0.002) 0.27 (0.002) 0.23 (0.006) 0.23 (0.008) East 0.22 (0.002) 0.23 (0.002) 0.16 (0.005) 0.11 (0.006) North 0.18 (0.002) 0.18 (0.002) 0.17 (0.006) 0.18 (0.007) South 0.34 (0.002) 0.33 (0.002) 0.45 (0.007) 0.48 (0.010) Urbanzaton (% of sample) Small ctes & rural areas 0.75 (0.002) 0.74 (0.002) 0.77 (0.006) 0.81 (0.008) Large cty ( 100,000 nhabtants) 0.35 (0.002) 0.32 (0.002) 0.35 (0.007) 0.40 (0.009) Household sze & Kds (sample means or % of sample) Household sze (sample mean) 2.46 (0.005) 2.47 (0.005) 2.42 (0.017) 2.31 (0.022) total number of kds (sample mean) 0.51 (0.003) 0.52 (0.004) 0.47 (0.012) 0.46 (0.015) Kds between 0 and 7 years (%) 0.14 (0.001) 0.14 (0.001) 0.15 (0.005) 0.17 (0.007) Educaton b) (% of sample) Educaton level (0.002) 0.30 (0.002) 0.23 (0.006) 0.16 (0.007) Educaton level (0.002) 0.28 (0.002) 0.23 (0.006) 0.22 (0.008) Hgh school dploma 0.18 (0.002) 0.18 (0.002) 0.18 (0.006) 0.19 (0.008) Unversty degree 0.25 (0.002) 0.24 (0.002) 0.35 (0.007) 0.43 (0.010) Age (% of sample) < 30 years 0.08 (0.001) 0.08 (0.001) 0.07 (0.004) 0.07 (0.005) years 0.43 (0.002) 0.43 (0.002) 0.40 (0.007) 0.45 (0.010) years 0.37 (0.002) 0.37 (0.002) 0.40 (0.007) 0.38 (0.009) 70 years 0.12 (0.001) 0.12 (0.001) 0.13 (0.005) 0.10 (0.006) Professon (% of sample) Employees & Publc servants 0.43 (0.002) 0.42 (0.002) 0.45 (0.007) 0.54 (0.010) Workers & Apprentces 0.15 (0.001) 0.16 (0.002) 0.10 (0.005) 0.06 (0.005) Freelancers & Self-employed 0.05 (0.001) 0.05 (0.001) 0.06 (0.003) 0.06 (0.005) Housewves, Pensoners & Students 0.33 (0.002) 0.33 (0.002) 0.36 (0.007) 0.32 (0.009) Jobless persons 0.04 (0.001) 0.04 (0.001) 0.03 (0.003) 0.02 (0.003) No. of observatons 64,385 57,292 4,427 2,666 % of observatons No. of households 22,885 14,982 6,839 1,064 a) The net ncome s computed as the equvalent household dsposable ncome. Household members are weghted pursuant to the OECD equvalence scale. b) Educaton levels are defned accordng to the German schoolng system: level 1 Hauptschulabschluss, level 2 Realschulabschluss, level 3 Abtur (unversty-entrance dploma), level 4 unversty degree. Source: Own computaton on the bass of GfK Consumer Scan panel data,

8 Demand s analyzed on an annual data bass. The sample conssts of 22,885 mlk consumng households 5 and 64,385 observatons. Table 2 provdes nformaton on the sample demographc dstrbuton. The average weghted per-capta ncome 6 s about 1,320 Euro and the average household sze s 2.5. The majorty of households s of German natonalty (94 %) and lves n the South (34 %). In 64 % of the reportng households a female person s manly responsble for food purchases. 48 % of the household heads are employed or self-employed; 43 % of them are n the age range of 30 and 49. On average, panelsts spent approxmately 3 % of ther mlk budget on organc mlk. Furthermore, table 2 gves frst hnts at the socodemographc profle of non-buyers of organc mlk, occasonal buyers and commtted buyers. Followng the classfcaton of BUDER et al. (2010), households are classfed nto three groups accordng to ther organc mlk budget share (OB plus OPL mlk): Non-buyers spend less than 1 %, occasonal buyers between 1 and 20% and commtted buyers more than 20% of ther mlk budget on organc mlk. In total, 14,982 households are classfed as non-buyers, 6,839 as occasonal buyers and 1,064 as commtted buyers. Comparng demographc nformaton across these consumer groups, table 2 shows that commtted buyers have on average a larger net ncome (1,531 Euro) than average mlk buyers (1,323 Euro). Moreover, there are regonal dfferences: Organc mlk buyers tend to lve n the south and n ctes. Besdes the ncome effect, ths fndng could be explaned by the fact that households located closer to central busness dstrcts have better access to organc food or may be more aware of healthy eatng or sustanable consumpton (SMITH, HUANG & LIN 2009, 740). Commtted buyers show a below average household sze and number of chldren but they are more lkely to have young chldren up to seven years of age. Commtted buyers are most lkely to be employees or cvl servants and most of them are mddle-aged. The share of households wth a unversty degree s well above average among commtted and occasonal buyers. 5 Results and Dscusson 5.1 Probt regressons Table 3 dsplays the results of the frst-step probt regresson n detal. The estmated coeffcents of probt models are dffcult to nterpret. In nonlnear models, margnal effects are often more nformatve than regresson coeffcents themselves (CAMERON & TRIVEDI 2009, 462). To allow for a more meanngful nterpretaton, elastctes wth respect to consumpton partcpaton are computed as ( P ( y > 0) / x) ( x / P) for the contnuous varables prce premum and habt formaton. For dscrete varables margnal effects wth respect to the consumpton partcpaton decson,.e., P ( y > 0), are reported. Equaton (5) s estmated for H=19,066 households and T=4 years 7. The results confrm the mpacts of socodemographc characterstcs on consumers purchase decsons whch were postulated by descrptve statstcs. The hgher the ncome and the hgher the educatonal attanment, the more lkely s the household to buy OB, OPL and CB mlk. Havng a per-capta ncome of at least 2,250 Euro ncreases the probablty of purchasng OB (OPL, CB) mlk by 0.06 (0.04, 0.11 respectvely) relatve to a household wth an ncome of less than 750 Euro, ceters parbus. As expected, the mpact of ncome s hgher on OB mlk than on OPL mlk. 5 The panel s not balanced. Durng the sample perod some households entered and others left the panel. Therefore, the number of households n ths analyss exceeds the average panel sze of 20,000 households. 6 We appled the OECD-modfed equvalence scale frst proposed by HAAGENARS et al. (1994) to compute a weghted per-capta ncome. In the followng we refer to ths varable when talkng about ncome. 7 Because of the dependence on lagged consumpton the sample perod shortens and the number of households n the sample decreases. Consequently, the probt model s estmated for the perod from 2005 to

9 Table 3. Frst-step probt regressons: Whch factors determnate the probablty to buy organc and conventonal mlk? Probablty margnal effects a) and probablty elastctes b) of demographc varables, past consumpton and prce prema % User household of Obs. OB mlk OPL mlk CB mlk CPL mlk prce premum % prce premum ** *** ** --- < d d d d *** ** ncome *** *** *** ** *** *** *** > *** *** *** * educaton level d d d d educaton c) educaton level educaton level *** *** educaton level *** *** ** < 30 years 8.3 d d d d age years * *** years ** *** > 70 years * *** workers & apprentces 42.0 d d d d employees & publc servants *** *** * professon freelancers & self-employed ** * ** housewves, pensoners & students *** *** ** jobless persons ** ** natonalty German 93.0 d d d d (D naton ) others * * urbansaton others 67.4 d d d d (D cty ) large ctes ** *** ** sngle households mult-person household 79.0 d d d d (D sngle ) sngle household ** *** Number of no chld 68.6 d d d d chldren 1 chld * *** (<18 years) 2 chldren * (kds18) 3 and more chldren *** ** *** young chldren no chld under 7 years 85.7 d d d d (D kds07 ) chldren under 7 years *** *** *** Gender male 35.1 d d d d (D gender ) female *** ** * *** place of resdence (regon) west 26.2 d d d d east *** *** *** south *** *** *** *** north *** ** Quantty demanded n the prevous year (habt formaton) *** *** *** *** n (No. of observatons) 42,707 42,707 42,707 42,707 N (No. of households) 22,885 22,885 22,885 22,885 McFadden s Adj. R² Adj. Count-R² Note. ***, **, * and (*) denote sgnfcance at 0.1, 1, 5 and 10 %, respectvely; d denotes the dummy category not ncluded n the estmaton to avod dummy varable trap. a) Probablty margnal effect s reported for dscrete varables and denotes absolute change n organc mlk con sumpton partcpaton probablty n response to one level ncrease for the multlevel dscrete varables (ncome, educaton, age and kds18) or 0/1 change for the dummy varables. b) Probablty elastcty s used for contnuous varables and nterpreted as the percentage change n organc mlk consumpton partcpaton probablty n response to the percentage change n contnuous varable. c) Educaton levels are defned accordng to the German schoolng system: level 1 Hauptschulabschluss, level 2 Realschulabschluss, level 3 Abtur (unversty-entrance dploma), level 4 unversty degree. Source: Own computaton on the bass of GfK Consumer Scan panel data,

10 Furthermore, households where a female person s key household shopper, households lvng n large ctes and households wth young chldren show a hgher probablty to buy organc mlk. However, the probablty declnes when there s more than one chld n the household. The mpact of age on organc mlk consumpton partcpaton seems to be non-lnear. Mddleaged household heads are more lkely to buy organc mlk than younger (<30 years) and older households ( 70 years). Estmaton results also reveal regonal dfferences. For households located n the southern parts of Germany the probablty of purchasng OB, OPL and CB mlk ncreases by about 0.03, respectvely, relatve to households located n the west. As expected, prces and habt formaton are mportant determnants of the frst-step decson. On average, the percentage prce premum was 64 % for OB, 55 % for OPL and 32.5 % for CB mlk. Probablty elastctes n table 3 ndcate that as the prce premum of OPL mlk, for example, ncreases by one percentage pont, the probablty of purchasng OPL mlk lowers by 0.3 %. Interestngly, prce prema show a hgher mpact on the partcpaton decson wth respect to OPL and CB mlk than to OB mlk. The goodness of ft of the probt regressons s satsfactory. The adjusted Count-R², whch s the proporton of correct guesses beyond the number that would be correctly guessed by choosng the largest margnal (LONG and FREESE 2006, 110ff), s 15.8 %, 14.5 % and 8.5 % for the models explanng OB, OPL and CB mlk consumpton partcpaton, respectvely. 5.2 LA/AIDS estmaton Secton presents the second-step estmaton results for the whole sample. Secton gves a more detaled vew on dfferent consumer groups Pooled regressons for all consumers Presentng the second-step estmaton results, ths paper focuses on own-prce elastctes. Therefore, these elastctes wll be dscussed n most detal 8. Table 4 compares elastcty estmates of ths study to those of prevous studes presented n secton 2. The fact that prevous studes rarely acheved sgnfcant prce elastcty estmates for organc mlk s possbly caused by consderably smaller sample szes. Table 4. Comparson of uncompensated prce and ncome/ expendture elastctes n dfferent analyses of organc and conventonal mlk markets a) GLASER & THOMPSON (2000) DHAR & FOLTZ (2005) JONAS & ROOSEN (2008) MONIER et al. (2009) ALVIOLA & CAPPS (2010) CHOI & WOHGENANT (2010) Own results (2011) sample perod / country U.S. U.S. Germany France U.S. U.S. Germany own-prce elastcty CB mlk -0.73** -0.96* -0.93*** -1.04*** -1.02* -0.87*** ( * ) CPL mlk -0.66** -1.01* -0.42*** OB mlk -0.25** *** * *** OPL mlk -0.40** ncome/ expendture elastcty CB mlk 1.16** e) 0.99* e) *** e) CPL mlk 1.00** e) 0.97*** 1.04* e) ) 0.75 ( * ) e) ** e) OB mlk e) -5.73* e) 0.50*** 0.73* e) 0.27* ) 0.60 e) OPL mlk e) Note. ***, **, * and (*) denote sgnfcance at 0.1, 1, 5 and 10 %, respectvely. a) If there are several elastcty estmates for dfferent fat contents, here that one for whole mlk s shown; e) expendture elastcty; ) ncome elastcty; --- expendture or ncome elastctes were not computed. Source: Own complaton. 8 Tables showng the full estmaton results for the pooled estmaton and the estmaton segmented by consumer groups presented n the followng secton are avalable from the author on request. 9

11 Comparng the magntude of elastcty estmates of prevous studes there are three basc fndngs. Frst, demand for conventonal mlk s nelastc or slghtly elastc. Second, demand for organc mlk seems to be hghly elastc. Thrd, there s no sgnfcant dfference n prce elastcty between prvate-label and brand mlk. The present analyss confrms that demand for conventonal mlk s nelastc, but contradcts the other fndngs. Prce senstvty dffers substantally between brand and prvate-label mlk, both for conventonal and for organc mlk. Furthermore, the estmaton results of the present study ndcate an nelastc demand for organc mlk, both for OB mlk (-0.25) and for OPL mlk (-0.40). The dssmlarty n the magntude of own-prce elastcty estmates of ths study n comparson to prevous studes demands a closer look. Elastcty estmates have to be nterpreted wth regard to ther data base, estmaton procedure and sample perod. These factors can provde frst hnts at possble causes for dfferences n the magntude of prce elastcty estmates. Frst, most of the studes only consder general retalng or do not explctly state whether purchases n organc food shops are ncluded n the sample or not. However, organc food purchases are at least underrepresented when focussng on the general retalng and consumer prce senstvty s naturally lower n organc food shops than n other retal formats 9. Second, the sample perod dffers. GLASER and THOMPSON (2000, 15), who estmated demand elastctes separately for several perods, found that prce elastcty for organc mlk declned over tme, whereas prce elastctes for CB and CPL mlk remaned constant. Thus, takng nto account that the database of ths study s more recent and also ncludes purchases n organc food shops 10, t seems plausble that prce elastctes for organc mlk (n absolute values) are smaller. However, results show that nether the hgh degree of dsaggregaton - as argued by JONAS and ROOSEN (2008, 203) - nor the applcaton of AIDS - as stressed by GLASER and THOMPSON (2000, 17) - necessarly results n very elastc elastcty estmates for organc food products. Furthermore, the fact that demand for organc mlk s less elastc than demand for ts conventonal counterpart s feasble. Showng an absolute value of prce elastcty smaller than unty, demand for organc mlk resembles the demand for typcal staple foods. Prces play an mportant role as ndcated by the sgnfcance level and they show the expected sgn. However, prces do not mpact the quantty demanded as strong as they do for luxury goods. Hence, the result confrms the assumpton that organc products are usually consdered as necesstes and are often bought by convcton. Addtonally, there are fewer substtutes for organc mlk than for conventonal mlk. Supermarkets and especally dscounters typcally offer only one type of organc mlk mostly fresh whole fat mlk. If consumers am to buy organc mlk, a prce-nduced shft to long-lfe mlk or to mlk wth another fat content s not always possble wthn one place of purchase. Ths fact also leads to lower absolute own-prce elastcty estmates. The estmated expendture elastctes of ths study range about unty for all mlk types. Thus, a one-percentage ncrease n total mlk expendtures does not result n a consderable reallocaton of mlk budget shares between the mlk types. 9 Assumng that consumers who buy organc mlk by convcton often attend specalsed stores lke organc food shops, prce elastcty of organc mlk consumers n organc food shops s expected to be less elastc than prce elastcty of organc mlk consumers n other retal formats. 10 As a consequence of the ameloraton of the data wth respect to organc food, the data base of the present study s assumed to cover at least 66 % of the organc mlk market whle the GfK Homescan Panel data used by JONAS and ROOSEN (2008) represented only 36 % of the organc mlk sales (BIEN & MICHELS 2007, 12f). 10

12 5.2.2 Dfferentaton between consumer groups An nelastc demand mples that prce campagns at retal level are not the approprate nstrument to ncrease (organc) mlk sales. Ths concluson s based on the estmaton for the whole sample presented above. As estmated prce elastctes can lay the foundaton for decsons concernng prcng and dstrbuton strateges, t has to be proved whether prce senstvty s the same for all consumer groups. If not, t s mportant to dfferentate between consumers and to pay specal attenton to the groups of prme mportance for the organc mlk market and to those wth a rsng share n the populaton. But so far, there s a lack of elastcty estmates for separate household groups wth respect to organc mlk n Germany. Table 5 pctures the change n consumer preferences whch becomes notceable n the ncreasng share of occasonal and commtted organc mlk buyers. In 2008, commtted buyers made up 5.4 % of all households but accounted for more than 90 % of total organc mlk expendtures. In contrast, 87 % of the populaton were stll non-buyers. Hence, for the future development of the organc mlk market, t seems to be especally mportant to acqure ths consumer group. Table 5. Percentage shares of consumer groups wth respect to organc mlk expendture shares n Germany, Consumer group Non-buyers 92.2% 91.7% 89.0% 86.5% 87.1% Occasonal buyers 5.4% 5.5% 6.9% 8.3% 7.5% Commtted buyers 2.4% 2.7% 4.1% 5.2% 5.4% Note: Households are classfed accordng to ther organc mlk budget share: Non-buyers spend less than 1 %, occasonal buyers between 1 and 20% and commtted buyers more than 20% of ther mlk budget on organc mlk. Source: Own computaton on the bass of GfK Consumer Scan panel data, In fgure 1 the absolute value of the own-prce elastcty estmate s plotted for dfferent consumer groups. Expectedly, households that are used to buyng organc mlk,.e. commtted buyers, are less prce-senstve wth respect to the organc mlk prce than non-buyers and occasonal buyers (cf. fgure 1, rght sde). On the other hand, they are consderably more prce-senstve wth respect to the conventonal mlk prce (cf. fgure 1, left sde). The reverse s true for non-buyers. Whle the demand for conventonal mlk s nelastc among ths group, ther demand for organc mlk s slghtly elastc. Fgure 1. Comparson of own-prce elastctes for organc and conventonal mlk between dfferent consumer groups n Germany, Conventonal mlk Organc mlk CB 0.8 OB CPL 0.4 OPL non-buyers occasonal buyers ntensve buyers 0.0 non-buyers occasonal buyers ntensve buyers prvate-label mlk brand mlk. Note: Non-buyers are defned as households that spend less than 1 %, occasonal buyers between 1 and 20 % and commtted buyers more than 20 % of ther mlk budget on organc mlk. Source: Own computaton on the bass of GfK Consumer Scan panel data,

13 These fndngs mply two mportant facts: Frst, when makng marketng decsons t s very mportant to clearly defne the target group. Hence, prce promotons wth respect to organc mlk wll not ncrease sales among current consumers,.e. occasonal and commtted buyers. But a slghtly elastc demand of current non-buyers mples that prce reductons mght attract new consumers to organc mlk and mght ncrease ther expendtures on organc mlk. Bearng n mnd that non-buyers account for 87 % of all households n 2008 (see table 5), prce promotons at retal level seems to be promsng, especally n shops that are mostly frequented by non-buyers,.e. n general retalng. Second, the dfferent magntude of own-prce elastcty n several consumer groups underlnes that the use of average prce elastctes for the populaton as a whole s problematc for the projecton of future organc mlk demand f there are sgnfcant changes n populaton structure or consumer preferences. 6 Conclusons and outlook A growng number of studes deal wth consumer decsons concernng organc food. However, only few provde quanttatve estmates of demand elastctes. Ths paper contrbutes to the body of lterature by provdng own-prce elastcty estmates as well as analyss of the socodemographc determnants of demand for organc mlk n Germany. In (a) usng up-todate data, (b) dstngushng between dfferent consumer groups, (c) ncorporatng socodemographc varables of the households and (d) relyng upon a consderably large sample sze ths study s both an update and a refnement of prevous research. Applyng a two-step analyss, both the lkelhood of consumpton partcpaton and the consumpton levels are analyzed usng the GfK Homescan Panel data. Consumer prce senstvty s estmated separately for dfferent mlk types and for dfferent consumer groups n Germany. The dscrmnaton between brand and prvate-label products, both for conventonal and for organc mlk, provdes a more detaled vew on the characterstcs and behavour of organc consumers and non-consumers. Moreover, the tradtonal LA/AIDS was refned threefold by ncorporatng socodemographc determnants, by consderng dynamc aspects of mlk demand and by accountng for censorng. The fndngs of the frst-step probt analyss suggest that the prmary organc mlk consumer s well educated, wealthy and wthout chldren lvng n the household. Ths consumer tends to lve n the southern parts of Germany and n urban areas. Addtonally, prces and habt formaton are man determnants of the decson to buy or not to buy organc mlk. Low prce elastctes n the second step ndcate that once the decson to buy organc mlk s made, prce does not play an mportant role. Ths result s contradctory to pror studes. Whle demand for organc mlk n prevous research was found to be hghly elastc, the present analyss suggests that the demand for organc mlk n Germany s absolutely prcenelastc. Ths fndng mples that the structural change n the organc mlk market and n consumer preferences over the last few years result n lower consumer prce senstvty. Consequently, prevous research can not be used wthout reservaton for current market analyss. Furthermore, an nelastc demand suggests that prce campagns at retal level are not the rght nstrument to ncrease sales and to facltate growth. However, prce senstvty s not the same for all consumer groups. Current non-buyers show a consderably hgher prce responsveness wth respect to the organc mlk prce than households that already purchase organc mlk. The combnaton of the frst-step and the second-step results clearly reveal that there s a consderable potental to expand the organc mlk market by attractng new consumers. But there s lttle potental to enhance the quantty demanded by extant consumers by reducng prces. 12

14 References ALVIOLA, P.A. and O. CAPPS, JR. (2010): Household Demand Analyss of Organc and Conventonal Flud Mlk n the Unted States Based on the 2004 Nelsen Homescan Panel. In: Agrbusness 26 (3), BIEN, B. and P. MICHELS (2007): Aufbau ener kontnuerlchen Berchterstattung zum Enkaufsverhalten be ökologsch erzeugten Produkten n Deutschland unter Enbezehung der Ergebnsse aus dem BÖL-Projekt 02OE367. Fnal report of research project 02OE367/F of the German Bundesprogramm Ökologscher Landbau. BÖLW Bund Ökologsche Lebensmttelwrtschaft e.v. - (2009): Zahlen, Daten, Fakten: De Bo-Branche Berln. - (2010): Zahlen, Daten, Fakten: De Bo-Branche Berln. BRUHN, M. (2002): De Nachfrage nach Boprodukten. Ene Langzetstude unter besonderer Berückschtgung von Verbraucherenstellungen. Peter Lang, Frankfurt a.m. BUDER, F.; HAMM, U.; BICKEL, M.; BIEN, B. and P. MICHELS (2010): Dynamk des Kaufverhaltens m Bo-Sortment. Fnal report of research project 2809OE014 of the German Bundesprogramm Ökologscher Landbau. BUZBY, J.C. and J.R. SKEES (1994): Consumer Want Reduced Exposure to Pestcdes on Food - Chartng the Costs of Food Safety. In: Food Revew 17 (2), CAMERON, A.D. and P.K. TRIVEDI (2009): Mcroeconometrcs Usng Stata. Stata Press, Texas. CHOI, H.-J and M. WOHLGENANT (2010): The Welfare Effect of Organc Mlk. Selected Paper prepared for presentaton at the Agrcultural & Appled Economcs Assocaton 2010, July 25-27, Colorado. COX, T.L. and M. WOHLGENANT (1986): Prce and qualty effects n cross-sectonal demand analyss. In: Amercan Journal of Agrcultural Economcs 68 (4), DEATON, A. and J. MUELLBAUER (1980): An Almost Ideal Demand System. In: The Amercan Economc Revew 70 (3), DEMERITT, L. (2004): Organc Pathways. In: [N]Sght magazne. Hartman Group, Inc. Bellevue, WA. DETTMANN, R. and C. DIMITRI (2010): Who's Buyng Organc Vegetables? Demographc Characterstcs of U.S. Consumers. In: Journal of Food Products Marketng 16 (1), DHAR, T. and J.D. FOLTZ (2005): Mlk by any other name Consumer benefts from labelled mlk. In: Amercan Journal of Agrcultural Economcs 87 (1), DIMITRI, C. and K.M. VENEZIA (2007): Retal and Consumer Aspects of the Organc Mlk Market. U.S. Department of Agrculture, ERS LDP-M , Washngton, DC. GLASER, K. and G.D. THOMPSON (2000): Demand for Organc and Conventonal Beverage Mlk. Paper presented at the WAEA Annual Meetng 2000, June 29 July 1, Vancouver, Brtsh Columba. GOULD, B.W.; COX, T.L. and F. PERALI (1991):Demand for Food Fats and Ols: The Role of Demographc Varables and Government Donatons. In: Amercan Journal of Agrcultural Economcs 73 (1), GOVINDASAMY, R. and J. ITALIA (1999): Predctng Wllngness-to-Pay a Premum for Organcally Grown Fresh Produce. In: Journal of Food Dstrbuton Research 30, GREEN, R. and J. ALSTON (1990): elastctes n AIDS models. In: Amercan Journal of Agrcultural Economcs 72 (2), HAGENAARS, A., DE VOS, K. and M.A. ZAIDI (1994): Poverty Statstcs n the Late 1980s: Research Based on Mcro-data. Offce for Offcal Publcatons of the European Communtes. Luxembourg. HANSEN, G. (1993): Quanttatve Wrtschaftsforschung. Vahlen, München. 13

15 HILL, H. and F. LYNCHEHAUN (2002): Organc mlk: atttudes and consumpton patterns. In: Brtsh Food Journal 104 (7), HUGHNER, R.S.; MCDONAGH, P.; PROTHERO, A.; CLIFFORD, J.S. and J. STANTON (2007): Who are organc food consumers? A complaton and revew of why people purchase organc food. In: Journal of Consumer Behavour 6, JONAS, A. and J. ROOSEN (2008): Demand for Mlk Labels n Germany: Organc Mlk, Conventonal Brands and Retal Labels. In: Agrbusness 24 (2), LI, J.; ZEPEDA, L. and W. GOULD (2007): The Demand for Organc Food n the U.S.: An Emprcal Assessment. In: Journal of Food Dstrbuton Research 38 (3), LONG, J.S. and J. FREESE (2006): Regresson Models for Categorcal and Lmted Dependent Varables Usng Stata. Stata Press, Texas. LZ Lebensmttel Zetung (2005): Mlchbauern warnen vor Nachahmern. In: Lebensmttel Zetung 57 (14), 50. Deutscher Fachverlag GmbH, Frankfurt am Man. MONIER, S.; HASSAN, D.; NICHÈLE, V. and M. SIMIONI (2009): Organc Food Consumpton Patterns. In: Journal of Agrcultural & Food Industral Organzaton, Vol. 7. Specal Issue: Qualty Promoton through Eco-Labellng, artcle 12. MOSCHINI, G. and D. MORO (1996): Structural change and demand analyss: a cursory revew. In: European Revew of Agrcultural Economcs 23 (3), PLAßMANN, S. and U. HAMM (2009): Kaufbarrere Pres? - Analyse von Zahlungsberetschaft und Kaufverhalten be Öko-Lebensmtteln. Fnal report of the research project 06OE119 of the German Bundesprogramm Ökologscher Landbau. RIEFER, A. and U. HAMM (2009): Veränderungen der Konsumntenstät von Öko-Lebensmtteln n Haushalten mt Kndern. In: MAYER, J. et al. (ed.): Werte Wege Wrkungen: Bolandbau m Spannungsfeld zwschen Ernährungsscherung, Markt und Klmawandel. Conference transcrpt of the 10 th Scentfc conference organc farmng, Vol. 2. Dr. Köster, Berln, p SHONKWILER, J.S. and S.T. YEN (1999): Two-step estmaton of a censored system of equatons. In: Amercan Journal of Agrcultural Economcs 81 (4), SMITH, T.A.; HUANG, C.L. and B.-H. LIN (2009): Does Prce or Income Affect Organc Choce? Analyss of U.S. Fresh Produce Users. In: Journal of Agrcultural and Appled Economcs 41 (3), THOMPSON, G.D. (1998): Consumer demand for organc foods: What we know and what we need to know. In: Amercan Journal of Agrcultural Economcs 80 (5), THOMPSON, G.D. and J. KIDWELL (1998): Explanng the Choce of organc produce, cosmetc defects, prces and consumer preferences. In: Amercan Journal of Agrcultural Economcs 80 (2), WICKENS, M.R. and T.S. BREUSCH (1988): Dynamc specfcaton, the long-run and the estmaton of transformed regresson models. In: The economc journal 98 (390), WIER, M.; JENSEN, K.O.; ANDERSEN, L.M. and K. MILLOCK (2008): The Character of Demand n Mature Organc Food Markets: Great Brtan and Denmark Compared. In: Food Polcy 33 (5), ZEPEDA, L. and J. LI. (2007): Characterstcs of Organc Food Shoppers. In: Journal of Agrcultural and Appled Economcs 39, ZHANG, F. HUANG, C.L.; LIN, B.-H and J.E. EPPERSON (2008): Modellng Fresh Organc Produce Consumpton wth Scanner Data: A Generalzed Double Hurdle Model Approach. In: Agrbusness 24 (4), ZMP Zentrale Markt- und Presberchtsstelle GMBH (2003): Bo-Frsche m LEH. Fakten zum Verbraucherverhalten. Materalen zur Marktberchterstattung, No. 45. ZMP-Verlag, Bonn. 14