Reasoning in Psychology Using Statistics Psychology

Social Science Reasoning Using Statistics Announcements Quizzes 1 & 2 are posted –Quiz 1 due last Fri (Feb 23) (you can take it late, but only once) –Quiz 2 due this Fri Jan 30 (11:59 pm) Don’t forget Exam 1 is coming up (Feb 4) –In class part – multiple choice, closed book –In labs part – open book/notes Today –Nuts and bolts of experimental & observational designs

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

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

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

Social Science Reasoning Using Statistics Example Issue: What is the best way to study for a test? –Cram the night before –Spread your studying out over several nights How could we investigate this question? –What research methods should we use?

Social Science Reasoning Using Statistics ObservationalExperimental Selecting your research method Issue: What is the best way to study for a test? –involve manipulation of variables –involve examining variables as they already are How could we investigate this question? –What research methods should we use?

Social Science Reasoning Using Statistics ObservationalExperimental Example –Randomly select individuals –Watch their study habits –See how they do on a test –Randomly select individuals –Randomly assign to groups Crammed study group Distributed study group –See how they do on a test Issue: What is the best way to study for a test?

Social Science Reasoning Using Statistics Experimental Experiments –Randomly select individuals –Randomly assign to groups Crammed study group Distributed study group –See how they do on a test All experiments must make some sort of comparison. Why random assignment? How do it?

Social Science Reasoning Using Statistics Experiment ?? If only one group: Experiments Randomly select individuals Tell 10 students to distribute their studying See how they do on a test All experiments must make some sort of comparison. Why? –There is natural variability in your DV. –No comparison group, so can’t see if: change in the DVchange in the IV –Should not make causal claims” This is an observational design - called “one-shot case study design” Special case: when our “comparison” group is the population

Social Science Reasoning Using Statistics If two groups: Experiments Experiment All experiments must make some sort of comparison. Why? –Still some natural variability in your DV. –But have constrained one source of the variability (crammed or distributed studying) –Can see if there is an effect of the manipulation change in the DVchange in the IV Randomly select individuals Randomly assign to groups –Crammed study group –Distributed study group See how they do on a test –The systematic reduction and control of variability of the IV(s) allows us to examine whether they are sources of (causes) variability in the DV

Social Science Reasoning Using Statistics If two groups: Experiments Experiment All experiments must make some sort of comparison. Why? –Still some natural variability in your DV. –But have constrained one source of the variability –Can see if there is an effect of the change change in the DVchange in the IV Randomly select individuals Randomly assign to groups –Crammed study group –Distributed study group See how they do on a test –The systematic reduction and control of variability of the IV(s) allows us to examine whether they are sources of (causes) variability in the DV Have stronger footing on which to make causal claims Have stronger footing on which to make causal claims Evidence

Social Science Reasoning Using Statistics Example Issue: What is the best way to study for a test? Variables –Independent –Dependent –Extraneous Control Random Confound Experiment Randomly select individuals Randomly assign to groups –Crammed study group –Distributed study group See how they do on a test

Social Science Reasoning Using Statistics Experiment Randomly select individuals Randomly assign to groups –Crammed study group –Distributed study group See how they do on a test Example Issue: What is the best way to study for a test? – these are the variables that are manipulated by the experimenter 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 –Dependent –Extraneous Control Random Confound

Social Science Reasoning Using Statistics Example Issue: What is the best way to study for a test? Variables –Independent –Dependent –Extraneous Control Random Confound 1 IV (factor): study type 2 levels: Crammed study Study all in one night Distributed study Study over five nights Experiment Randomly select individuals Randomly assign to groups –Crammed study group –Distributed study group See how they do on a test

Social Science Reasoning Using Statistics Example Issue: What is the best way to study for a test? Variables –Independent –Dependent –Extraneous Control Random Confound Experiment Randomly select individuals Randomly assign to groups –Crammed study group –Distributed study group See how they do on a test – these are the variables that are measured by the experimenter, they are “dependent” on the independent variables

Social Science Reasoning Using Statistics Example Issue: What is the best way to study for a test? Variables –Independent –Dependent –Extraneous Control Random Confound Test performance Experiment Randomly select individuals Randomly assign to groups –Crammed study group –Distributed study group See how they do on a test

Social Science Reasoning Using Statistics Example Issue: What is the best way to study for a test? Variables –Independent –Dependent –Extraneous Control Random Confound Experiment Randomly select individuals Randomly assign to groups –Crammed study group –Distributed study group See how they do on a test – Holding things constant -Controls for excessive random variability -Examples?

Social Science Reasoning Using Statistics Experiment Example Randomly select individuals Randomly assign to groups –Crammed study group –Distributed study group See how they do on a test Issue: What is the best way to study for a test? Variables –Independent –Dependent –Extraneous Control Random Confound Crammed study Study for 5 hours Distributed study Study for 1 hour each night Total study time = 5 hours

Social Science Reasoning Using Statistics Experiment Example Randomly select individuals Randomly assign to groups –Crammed study group –Distributed study group See how they do on a test Issue: What is the best way to study for a test? Variables –Independent –Dependent –Extraneous Control Random Confound - May freely vary, to spread variability equally across all experimental conditions - Examples?

Social Science Reasoning Using Statistics Experiment Example Randomly select individuals Randomly assign to groups –Crammed study group –Distributed study group See how they do on a test Issue: What is the best way to study for a test? Variables –Independent –Dependent –Extraneous Control Random Confound

Social Science Reasoning Using Statistics Experiment Example Randomly select individuals Randomly assign to groups –Crammed study group –Distributed study group See how they do on a test Issue: What is the best way to study for a test? Variables –Independent –Dependent –Extraneous Control Random Confound – Other variables, that haven’t been accounted for (manipulated, measured, randomized, controlled) that co-vary with the IV(s) and can impact changes in the dependent variable(s) Sometimes called “lurking variables.” Examples?

Social Science Reasoning Using Statistics Experiment Example Randomly select individuals Randomly assign to groups –Crammed study group –Distributed study group See how they do on a test Issue: What is the best way to study for a test? Variables –Independent –Dependent –Extraneous Control Random Confound Crammed study Studied vocabulary and practice problems Distributed study Studied only vocabulary Test performance 85%73% Underlying third variable that varies with the IV Is this difference due to study method? Or is it due to what was studied?

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

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

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

Social Science Reasoning Using Statistics Wrap up Today’s lab –Practice developing and evaluating experiments Questions?