Experiment Basics: Variables

1. Experiment Basics: Variables Psych 231: Research Methods in Psychology

2. So you want to do an experiment? • You’ve got your theory. • What is the behavior/cognitive process that you want to examine? • What do you think affects that behavior/cognitive process?

3. So you want to do an experiment? • You’ve got your theory. • Next you need to derive predictions from the theory. • These should be stated as hypotheses. • In terms of conceptual variables or constructs

4. So you want to do an experiment? • You’ve got your theory. • Next you need to derive predictions from the theory. • Now you need to design the experiment. • Now you need to operationalize your variables in terms of how they will be: • Controlled • Manipulated • Measured • Be aware of the underlying assumptions connecting your constructs to your operational variables

5. An example • Hypothesis: Eating candy with peanuts improve memory performance • How might we test this with an experiment?

6. Constants vs. Variables • Characteristics of the psychological situations • Constants: have the same value for all individuals in the situation • Variables: have potentially different values for each individual in the situation • Constants: • M&Ms are eaten • Variables: • Type of M&M: peanut vs plain • Memory performance

7. Underlying assumptions Variables • Conceptual vs. Operational • Conceptual variables (constructs) are abstract theoretical entities • Operational variables are defined in terms within the experiment. They are concrete so that they can be measured or manipulated Conceptual Peanut candies Memory Operational Peanut M&Ms Memory test

8. Variables • Independent variables (explanatory) • Dependent variables (response) • Extraneous variables • Control variables • Random variables • Confound variables

9. Independent Variables • The variables that are manipulated by the experimenter (sometimes called factors) • Each IV must have at least two levels • Remember the point of an experiment is comparison • Combination of all the levels of all of the IVs results in the different conditions in an experiment

10. Factor A Condition 1 Condition 2 Factor A Cond 1 Cond 2 Cond 3 Factor B Cond 1 Cond 2 Cond 3 Factor A Cond 4 Cond 5 Cond 6 Independent Variables • 1 factor, 2 levels • 1 factor, 3 levels • 2 factors, 2 x 3 levels

11. Choosing your independent variable • Methods of manipulation • Straightforward manipulations • Stimulus manipulation - different conditions use different stimuli • Instructional manipulation– different groups are given different instructions • Staged manipulations • Event manipulation– manipulate characteristics of the context, setting, etc. • Subject manipulations – there are (pre-existing mostly) differences between the subjects in the different conditions (leads to a quasi-experiment)

12. Peanut M&Ms Plain M&Ms Bottlecaps Choosing your independent variable • What about our candy experiment? 1 IV: Candy type (3 levels)

13. Dependent Variables • The variables that are measured by the experimenter • They are “dependent” on the independent variables (if there is a relationship between the IV and DV as the hypothesis predicts).

14. Choosing your dependent variable • How to measure your your construct: • Can the participant provide self-report? • Introspection – specially trained observers of their own thought processes, method fell out of favor in early 1900’s • Rating scales – strongly agree-agree-undecided-disagree-strongly disagree • Is the dependent variable directly observable? • Choice/decision (sometimes timed) • Is the dependent variable indirectly observable? • Physiological measures (e.g. GSR, heart rate) • Behavioral measures (e.g. speed, accuracy)

15. Choosing your dependent variable • What about our candy experiment? • Conceptual level:Memory • Operational level: Some kind of memory test • Memorize a list of words while eating the candy • Then 1 hour after study time, recall the list of words • Measure the accuracy of recall

16. Extraneous Variables • Control variables • Holding things constant - Controls for excessive random variability • Number of M&Ms consumed • Time of day test taken

17. Extraneous Variables • Random variables – may freely vary, to spread variability equally across all experimental conditions • Randomization • A procedures that assure that each level of an extraneous variable has an equal chance of occurring in all conditions of observation. • On average, the extraneous variable is not confounded with our manipulated variable. • What your participants ate before the • experiment

18. Control your extraneous variable(s) • Can you keep them constant? • Should you make them random variables? • Two things to watch out for: • Experimenter bias (expectancy effects) • the experimenter may influence the results (intentionally and unintentionally) • E.g., Clever Hans • One solution is to keep the experimenter “blind” as to what conditions are being tested • Demand characteristics – cues that allow the participants to figure out what the experiment is about, influencing how they behave

19. Confound Variables • Confound variables • Other variables, that haven’t been accounted for (manipulated, measured, randomized, controlled) that can impact changes in the dependent variable(s)

20. Next time • Read chapters 4 & 5. • Bring your textbook and/or APA Publication Manual to lab (if you’ve got one) • Don’t forget your first journal summary is due this week in lab

21. Exam Average = 81.8 • Range: 58 - 95