1Introduction to Social Psychology:MethodsPsy 240; Fall 2006Purdue UniversityDr. Kipling WilliamsPsy 240: Williams 2Example 1• Individuals primed with “old people concepts”are more likely to walk slower than those whoare not primed with “old people concepts.”• Independent variable– Operationally define “old people concepts”• Dependent variable– Operationally define “walking speed.”2Psy 240: Williams 3Example 1: GraphPsy 240: Williams 4Example 1: Graph3Psy 240: Williams 5Example 2: Identifiability andSocial Loafing• Hypothesis: Individual task performance willdecline as group size increases, especiallywhen individuals’ contributions to the groupeffort are unidentifiable.– Rationale: diffusion of responsibility, loss ofevaluation potentialPsy 240: Williams 6Example 2: Between andWithin-S factors4Psy 240: Williams 7Within-S factors• Each participant experiences all levels of thewithin-S factor (e.g., working…[group size])• Their order becomes a concern to the internalvalidity of the experiment.– There may be fatigue or practice effects– Thus, order must be random or counter-balanced• Because participants experience all levels,they may guess the what is important in thestudy, trying to figure out hypothesis.– Demand characteristicsPsy 240: Williams 8Between-S factors• Each participant experiences only one level ofthis factor (e.g., identifiability/unidentifiability)• Participants must be randomly assigned tothe level of this factor.– Any other method of assignment violatesassumptions of statistical tests, and threatensinternal validity• Examples: morning/afternoon5Psy 240: Williams 9Example 2: Between andWithin-S factors• Independent Variables?– Operational definitions• Dependent Variables?– Operational definitions• Main effects?• Interactions?• Internal Validity?• External Validity?Psy 240: Williams 10Example 3: Stealing Thunder• Revealing the worst evidence aboutyour client before the prosecutorreveals it reduces the negative impactof that evidence.– Rationale: increases credibility, causes re-evaluation of the meaning of the evidence.6Psy 240: Williams 11Example 3: Stealing ThunderPsy 240: Williams 12Example 3: Stealing Thunder• Independent variables?– Operational definitions• Dependent variable?– Operational definitions• Within or Between?• Main effects orinteractions?• Internal validity• External