Correlation & Experimentation

Module 6 6-1 Describe positive and negative correlations, and explain how correlational measures can aid the process of prediction but not provide evidence of cause-effect relationships. 6-2 Explain illusory correlations. 6-3 Describe the characteristics of experimentation that make it possible to isolate cause and effect.

Correlation A measure of the extent to which two variables change together, and thus of how well either variable predicts the other Correlation coefficient is a statistical index of the relationship between two variables ranging from -1.0 to +1.0

IMPORTANT POINT… Positive vs. Negative This is the first of many times where these terms will be used in this class. You MUST get over thinking of these terms as indicators of “good” & “bad” because in this class they will often mean other things. E.G.: In correlations, they merely indicate direction of the correlation and have NOTHING to do with the desirability of the relationship between the variables.

Positive (“direct”) & Negative (“inverse”) Test YOUR understanding of correlation. Is it + or -?? The more children and youth used various media, the less happy they were with their lives. Negative The less sexual content teens saw on TV, the less likely they were to have sex. Positive The longer children were breast-fed, the greater their later academic achievement. The more income rose among a sample of poor families, the few psychiatric symptoms their children experienced.

Correlation does NOT equal causation! Self-esteem correlates negatively (strongly) with depression.

Active Learning Go to a news website and find reports about psychological studies. Evaluate the articles using the info we have covered so far and using the following questions as guidelines: What was the hypothesis of the study? Who were the participants in this study? Is this population representative of people in general? If possible, how was sample obtained? Is this study Correlational? If so what variables are related? Does the article make it seem like the results are due to a cause & effect relationship?

Illusory Correlations The phenomenon of perceiving a relationship between variables (typically people, events, or behaviors) even when no such relationship exists Confirmation Bias: we often seek only the evidence that confirms our beliefs & ignore any that goes against them!

Experimentation This is the ONLY way to determine cause & effect…. Unlike Correlational studies, in experiments we manipulate variables… Experimental vs Control Dependent vs Independent (& Confounding) Random sampling vs Random assignment Single-blind procedure vs Double-blind procedure Placebo effect:

Validity: the extent to which a test or experiment measures or predicts what it is supposed to Construct validity: Do the variables represent or measure what they are supposed to measure? Predictive validity: How well do the variables measured predict other measures of the same construct? Internal validity: How well constructed was the experiment to control for confounding variables? External validity: How well do the results of the experiment translate to other settings or partipants?

The OREO Experiment Hypothesis: OREOs improve memory. Step 1: Random assignment Step 2: Control vs Experimental groups Step 3: Memory Test Step 4: Results PROBLEMS?????