Saarland University Proseminar Human-Computer Interaction Antonia Scheidel! May 14th, 2009 USABILITY I Introducing
31 Tullis & Albert: Chapters 1 + 2 Antonia Scheidel! Proseminar HCI! May 14th 2009! I
32 Overview What is? Why does matter? Antonia Scheidel! Proseminar HCI! May 14th 2009! I
3 - Definition ISO 9241-11: the extent to which a product can be used by specified users to achieve specified goals with effectiveness, efficiency and satisfaction in a specified context of use Antonia Scheidel! Proseminar HCI! May 14th 2009! I
4 Why does matter? Antonia Scheidel! Proseminar HCI! May 14th 2009! I
5 Why does matter? (cont.) Because the design of a product should not Disqualify groups of people from using the product Keep people from using the product for its / their intended purpose Be the cause for inconvenience or frustration for the user Antonia Scheidel! Proseminar HCI! May 14th 2009! I
6 Measuring " Measure effectiveness, efficiency and user satisfaction. Two ways to go: Trust your own judgement / gut feeling / design department Take advantage of usability metrics when evaluating a new product Antonia Scheidel! Proseminar HCI! May 14th 2009! I
6 Measuring " Measure effectiveness, efficiency and user satisfaction. Two ways to go: Trust your own judgement / gut feeling / design department Take advantage of usability metrics when evaluating a new product! Antonia Scheidel! Proseminar HCI! May 14th 2009! I
7 Why use? Intuition is important, but data are better Compare usability of two products Classify the magnitude of a problem Make predictions about the actual use of your product Provide management with facts and figures Antonia Scheidel! Proseminar HCI! May 14th 2009! I
8 Desired qualities: should be Observable (task completion - Y/N) Quantifiable Example: 90% of the users are able to complete a set of tasks in less than one minute. Antonia Scheidel! Proseminar HCI! May 14th 2009! I
9 Designing a Study 1. Select Participants: Are they representative? Separate them into gender, age (..) groups Decide on sampling strategy 2. Choose Sample Size: How much is enough? Antonia Scheidel! Proseminar HCI! May 14th 2009! I
10 Designing a Study II 3. Within-Subjects or Between-Subjects? One user - many tasks Multiple groups - one task each 4. Counterbalancing: Randomize! (Don t stick to one task order) Antonia Scheidel! Proseminar HCI! May 14th 2009! I
11 Know your Four types of data: Nominal (categories) Ordinal (ranks) Interval Ratio Antonia Scheidel! Proseminar HCI! May 14th 2009! I
12 Nominal Unordered categories Examples: Men and women Windows and Mac Users Users from France, Germany, the UK Antonia Scheidel! Proseminar HCI! May 14th 2009! I
13 Ordinal Ordered categories " rankings Example: Severity ranking # poor # fair # good # excellent Differences between measurements are not meaningful! Antonia Scheidel! Proseminar HCI! May 14th 2009! I
14 Interval Differences between measurements are meaningful! Example: poor # # # # excellent No natural zero Antonia Scheidel! Proseminar HCI! May 14th 2009! I
15 Ratio Just like interval data, but: absolute zero point (ratio!) Examples: height, weight,... (task completion) time (user) age Antonia Scheidel! Proseminar HCI! May 14th 2009! I
16 How can you use your? Different types of data " different kinds of statistical operations available Nominal & Ordinal: Carry out! 2 tests, compute frequencies simplified Interval & Ratio: Descriptive statistics, t-test, ANOVA, compute correlation Antonia Scheidel! Proseminar HCI! May 14th 2009! I
17 Tests: Chi-Square (! 2 ) For nominal and ordinal data Compare expected results to observed results Used to determine: goodness of fit (in)dependence of variables Antonia Scheidel! Proseminar HCI! May 14th 2009! I
18! 2 -Test: Example Are hair colour and eye colour independent variables? Antonia Scheidel! Proseminar HCI! May 14th 2009! I
19 Descriptive Statistics Antonia Scheidel! Proseminar HCI! May 14th 2009! I
19 Descriptive Statistics Antonia Scheidel! Proseminar HCI! May 14th 2009! I
19 Descriptive Statistics Antonia Scheidel! Proseminar HCI! May 14th 2009! I
19 Descriptive Statistics Antonia Scheidel! Proseminar HCI! May 14th 2009! I
19 Descriptive Statistics Antonia Scheidel! Proseminar HCI! May 14th 2009! I
19 Descriptive Statistics Antonia Scheidel! Proseminar HCI! May 14th 2009! I
19 Descriptive Statistics Antonia Scheidel! Proseminar HCI! May 14th 2009! I
19 Descriptive Statistics Antonia Scheidel! Proseminar HCI! May 14th 2009! I
20 Comparing Means...... based on Independent Samples Between-Subjects design: different groups, one task Example: Find out whether there is a significant difference in the time men or women spend using our product. t-test: Two Samples Assuming Equal Variances Antonia Scheidel! Proseminar HCI! May 14th 2009! I
21 t-test: Example If this value is below a certain threshold (here: 0.05) Conclude that the difference is statistically significant. Antonia Scheidel! Proseminar HCI! May 14th 2009! I p-value
22 Comparing Means...... based on Paired Samples Within-Subjects design: One group, different tasks Example: Find out if your participants significantly prefer one design over another t-test: Paired Two Samples for Means Like before: Evaluate p-value Antonia Scheidel! Proseminar HCI! May 14th 2009! I
22 Comparing Means...... based on Paired Samples Within-Subjects design: One group, different tasks Example: Find out if your participants significantly prefer one design over another t-test: Paired Two Samples for Means Like before: Evaluate p-value Antonia Scheidel! Proseminar HCI! May 14th 2009! I
23 What if there are more than two Variables? Solution: ANalysis Of Variance (ANOVA) Compare variances between and within groups Example: Given three designs: Is there a significant effect due to the different designs? Then: Use ANOVA results to carry out t-tests Antonia Scheidel! Proseminar HCI! May 14th 2009! I
24 Single Factor ANOVA: Example Antonia Scheidel! Proseminar HCI! May 14th 2009! I
25 Correlation Or: How strong is the relationship between two variables? R 2 = 0,58 Antonia Scheidel! Proseminar HCI! May 14th 2009! I
26 Bar Graphs Presenting your Results - I Antonia Scheidel! Proseminar HCI! May 14th 2009! I
27 Presenting your Results - II Line Graphs Antonia Scheidel! Proseminar HCI! May 14th 2009! I
28 Presenting your Results - III Scatterplots R 2 = 0,58 Antonia Scheidel! Proseminar HCI! May 14th 2009! I
29 Presenting your Results - IV Pie Charts Antonia Scheidel! Proseminar HCI! May 14th 2009! I
30 Stacked Bar Charts Presenting your Results - V Antonia Scheidel! Proseminar HCI! May 14th 2009! I
31 3 matters. Measuring usability will convince people to keep on funding your project. Choose your participants wisely. Know your data. Summary Use the right tests. Impress people with presentations. Antonia Scheidel! Proseminar HCI! May 14th 2009! I
Thank you for your attention! Antonia Scheidel! Proseminar HCI! May 14th 2009! I