ASSUMPTIONS OF A SCIENCE OF PSYCHOLOGY Realism –The world exists independent of observer Causality –Events (mental states and behavior) are caused by prior and current conditions Regularity –Cause-effect relationships are stable over time (even if collective relations are unique Discoverability –Those stable relationships (laws) can be learned through careful observation

GOALS OF A SCIENCE OF PSYCHOLOGY Discover stable relationships among conditions Develop theories that: –Explain (sets of) relationships –Generate hypotheses about new relationships Theories vary in level and completeness of explanation –Parsimony and Occam’s Razor –The “transparency-sufficiency” trade-off –She who predicts the most data with the fewest “parameters” wins

RELATIONS AMONG VARIABLES Range of possible “functional relations” –Coffee and reaction time –Meditation and memory –Anxiety and test performance positive negative linear +accell -accell complex curvilinear (nonmonotonic)

(mis)INTERPRETING RELATIONS Problem: Construct Validity The link between theoretical and “operational” variables Solution: Operational definitions Anxiety:scores on questionnaires Memory:number of items recalled Attention:instructions to stress Task A Intelligence:?

(mis)INTERPRETING RELATIONS Problem: correlation = causation A > B, B > A, or C > A & B Solution: Experimental method! Take charge and manipulate one circumstance –The Independent Variable(s) Measure its effect on behavior –The Dependent Variable(s)

CONTROLLING MISCELLANEOUS FACTORS Problem: Confounding Variables Other factors that “covary” with your Independent Variable Solution: Control! Keep those other variables constant If you can identify them ahead of time..

CONTROLLING MISCELLANEOUS FACTORS Problems with Control Variables Low external validity and generalization Hard to keep all relevant factors constant Solution: Randomization! Randomly assign participants / materials to conditions if possible Constrain it if necessary The larger the sample, the better