A Practical Guide to Quantitative Research

Transcription

1 A Practical Guide to Quantitative Research MichailTsikerdekis October2012 FacultyOfSociology SOC756ResearchMethods MasarykUniversity This work is licensed under a Creative Commons Attribution-ShareAlike 2.0 Generic License.

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3 Research Design (e.g., survey) Sampling Method (e.g., random sampling) Variable types (e.g., interval Data Analysis (e.g., statistical methods

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5 An adventure down the rabbit hole of quantitative research

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7 We need your excellent talent in this dire time of need. Help us understand what is happening to our galaxy. Why is it that the economy is shrinking? Why is it that our Siths don t buy stuff? Why is it that the dreadful Jedi don t contribute to our economy? Where is Darth Vader when we need him? Research Invitation

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9 So let s get down and dirty

10 What is it that you want to find? - Differences - Correlations - Building Models (e.g., regression)

11 Formulating Hypotheses Rough guidelines: Clear, Logical, Concise Describes a condition of causality or difference Needs to be falsifiable Example: The faster a guitarist can play, the louder the audience will be.

12 Palpatine s Questions Why is it that the economy is shrinking? Why is it that our Siths don t buy stuff? Why is it that the dreadful Jedi don t contribute to our economy?

13 Palpatine s Questions Why is it that the economy is shrinking? Why is it that our Siths don t buy stuff? Why is it that the dreadful Jedi don t contribute to our economy?

14 Hypotheses H1 1 : The salary of the Sith influences their average weekly purchases. H1 2 : [Ditto for the Jedi] H2: Siths have significantly higher salaries than Jedi. H0: Null hypothesis = There is no effect

15 Research Model Affiliation (e.g., Jedi) H2 Salary H1 Average Weekly Purchases

16 Retrieving Data for Our Research Run a survey Use interstellar database

17 Designing the Survey: Retrieving Demographics What is your sex? Male Female How old are you? years Do you consider yourself a Jedi or Sith? Jedi Sith

18 Which of the following describes best your main reason for going to the interstellar supermarket? - Buy components for my spaceship - Fight depression (Shopping Therapy) - See the new brands of lightsabers - Socializing - Other (Please specify) What is your annual salary? How many items you buy on average weekly?

19 Likert Scales

20 Launching our survey Medium (e.g., post office, , etc.) Method (e.g., probabilistic sampling) Sample size (e.g., 20 or 1000?) Ideal research: Random sampling or stratified random sampling 100 % response rate 0 missing answers

21 Low response rate? Keeter, Scott, Courtney Kennedy, Michael Dimock, Jonathan Best and Peyton Craighill Gauging the Impact of Growing Nonresponse on Estimates from a National RDD Telephone Survey. Public Opinion Quarterly. 70(5): Curtin, Richard, Stanley Presser and Eleanor Singer The Effects of Response Rate Changes on the Index of Consumer Sentiment. Public Opinion Quarterly 64(4): J. Scott Armstrong, Terry S. Overton Estimating Nonresponse Bias in Mail Surveys. Journal of Marketing Research 14,

22 Data Retrieved Case ID Affiliation Salary ($) Avg. weekly purchases 1 Jedi 25, Sith 120, Sith 90, Jedi 30, Sith 100, Jedi 50, Jedi 40, Sith 70,000 89

23 Types of data Dichotomous Nominal Ordinal Interval / Ratio

24 Types of analysis Univariate (1) Bivariate (2) Multivariate (3+)

25 Steps for statistical analysis Determine the types of data. Get descriptive statistics. Visualize data using graphs. Determine statistical test. Check assumptions. Proceed with the analysis. Follow up with post/hoc tests. Conclusion: Reject or fail to reject H0

26 Results Affiliation: Frequency - Percent Jedi: 4 50% Sith: 4 50% Purchases Arithmetic mean: Median: 55 Mode: 20?

27 Results - Salary Jedi Mean: 36,250 Sith Mean: 95,000

28 Statistical Significance: What is p? The probability of receiving a result as extreme as the one you got when the null hypothesis is true Probability ( Result given Null Hypothesis is true) Probability (Result H0 = true) P (R H0) or P(D H0) It is not the probability of H0 being true! That would be P(H0 D)

29 The Threshold Alpha (α) =.05 p <.10 Approaching significance p <.05 Significant p <.01 Extremely significant Two types of errors: Type I Type II

30 Statistical Significance: Example p =.04 = 4% There is a 4% chance of receiving the type of data that I have when the null hypothesis is true With an α =.05 the null hypothesis is rejected

31 How about p =.50? Does it support the null hypothesis (H0)?

32 Bivariate analysis H1 1 : Pearson's r =.996, p =.004 H1 2 : Pearson's r = -.198, p =.802 Other tests: Spearman's rho (ρ), Cramer's V & phi(φ)

33 Testing for differences H2: t (6) = , p =.002, r =.897 Other tests: T-test, Mann-Whitney U, ANOVA,

34 Conclusions A statistically significant difference was found between the salaries of Jedis and Siths, t (6) = , p =.002, r =.897. The effect is large. Furthermore, the weekly purchases were found to statistically depend on the salary but only for the case of the Sith, r =.996, p =.004. No statistical significance was achieved for the case of Jedi. In conclusion, Siths contribute more to the economy when their salaries are higher. There is a huge inequality between the salaries of Sith and Jedi, however it is unclear on whether this inequality has any effect on the shopping behavior of the Jedi.

35 Summary (1) Quantitative research is a linear process (usually); as such, each stage affects the next one. Hypotheses help define goals and guide the design of your research. Decisions on the survey design and especially type of variables that will be obtained affect the analysis and results. Decisions on the sampling method as well as sample size definitively affect the results!

36 Summary (2) In many cases, you the option of choosing different types of variables for measuring one parameter (e.g., age can be measured on a numerical, ordinal or even categorical level). The choice of statistical analysis should be guided by your hypotheses, variables, survey design, assumptions and other factors. Statistical significance (p) is dependent on sample size! Effect sizes are a more objective estimate for identifying on whether there is an effect or not.

37 Further Reading Davies, Máire Messenger Practical research methods for media and cultural studies : making people count Field, Andy Discovering Statistics Using SPSS (Introducing Statistical Method) Alain F. Zuur, Elena N. Ieno, Erik Meesters A Beginner's Guide to R (Use R!) Joris Meys, Andrie de Vries R for Dummies Kenneth Bordens, Bruce Barrington Abbott Research Design and Methods: A Process Approach