1. Reasoning in Psychology Using Statistics Psychology 138 2015

2. Social Science Reasoning Using Statistics Announcements Homework 1 due in labs today –Homework 2 will be posted later today – due next Wed. in lab Exam 1 in 2 wks (Sept 9) –In class part – multiple choice, closed book –In labs part – open book/notes Today –Finish Reliability & Validity discussion –Nuts and bolts of experimental & observational designs

3. Social Science Reasoning Using Statistics Dart board example Dart board represents Population of all possible scores Center represents the true score Collection of ‘darts’ is a sample of measurements The center of the sample is the estimate of the true score

4. Social Science Reasoning Using Statistics Dart board example Low variability/low bias Points are all close together (similar) & Centered on the target Reliable & valid measure

5. Social Science Reasoning Using Statistics Dart board example Low variability/high bias Points are all close together (similar) & NOT centered on the target Reliable but invalid measure

6. Social Science Reasoning Using Statistics Dart board example High variability/low bias Points are NOT all close together (dissimilar) & Centered on the target Valid but unreliable measure

7. Social Science Reasoning Using Statistics Dart board example High variability/high bias Points are NOT all close together (dissimilar) & NOT centered on the target Unreliable & invalid measure

8. Social Science Reasoning Using Statistics Designing your research Generally the process involves a number of steps: –identification of your research questions –identifying your variables –specify your hypotheses (how are the variables related to one another) –selecting a research design –collecting your data, analyzing your data –drawing conclusions from your data about your hypotheses Today’s focus

9. Social Science Reasoning Using Statistics Design Decision Tree Statistical tests Context Research design Measurement scale

10. Social Science Reasoning Using Statistics ObservationalExperimental Selecting your research method Issue: What is the best way to study for a test? How could we investigate this question? –What research methods should we use?

11. Social Science Reasoning Using Statistics ObservationalExperimental Example –How does this work? Issue: What is the best way to study for a test?

12. Social Science Reasoning Using Statistics If only one group: Experiments All experiments must make some sort of comparison. Why? –What are problems w/studying 1 group? –Should not make causal claims Special case: when our “comparison” group is the population

13. Social Science Reasoning Using Statistics If two groups: Experiments All experiments must make some sort of comparison. Why? –Advantages? change in the DV?change in the IV

14. Social Science Reasoning Using Statistics Example Issue: What is the best way to study for a test? Variables –Independent –Dependent –Extraneous Control Random Confound

15. Social Science Reasoning Using Statistics Example Issue: What is the best way to study for a test? A number of ways to manipulate your IV –Event/Stimulus manipulations – manipulate characteristics of the stimuli, context, etc. –Instructional manipulations – different groups are given different instructions –Subject manipulations – there are (pre-existing mostly) differences between the subjects in the different conditions (typically results in quasi- experimental designs) Variables –Independent What are these? Event/Stimulus Manipulations – Instructional Manipulations – Subject Manipulations – Example – 1 IV with 2 levels (crammed vs. distributed studying)

16. Social Science Reasoning Using Statistics Example Issue: What is the best way to study for a test? Variables –Dependent Example?

17. Social Science Reasoning Using Statistics Example Issue: What is the best way to study for a test? Variables –Extraneous Control – what do these do? Example? Random – what are these? Example? Confound - what are these? Example? –Sometimes confounds are known as ‘lurking variables’

18. Social Science Reasoning Using Statistics ObservationalExperimental Example Which research method is best? - Precise control possible - Precise measurement possible - Can make causal claims - May see patterns of complex behaviors - Good first step - May learn about something unexpected - Shouldn’t make causal claims - Directionality of the relationship isn’t known - Threats to internal validity due to lack of control - Sometimes the results are not reproducible - Artificial situations may restrict generalization to “real world” - Complex behaviors may be difficult to measure Advantages Disadvantages - it depends

19. Social Science Reasoning Using Statistics Design Decision Tree Your design largely determines your statistical analysis

20. Social Science Reasoning Using Statistics Design Decision Tree SPSS Your design largely determines your statistical analysis Which test do I use? Student’s often find this one of the hardest parts of the course – the key is understanding the context Which test do I use? Student’s often find this one of the hardest parts of the course – the key is understanding the context