Experimental Design: Single factor designsAnnouncementsExperimental designsSingle variable – One Factor designs1 factor - 2 levelsSlide 6Single variable – one FactorSlide 8Slide 9InterpolationExtrapolation1 Factor - multilevel experimentsSlide 131 factor - 3 levelsSlide 15Slide 16Relationship between Anxiety and PerformanceSlide 18Pair-wise comparisonsNext timeExperimental Design: Single factor designsPsych 231: Research Methods in PsychologyAnnouncementsReminder: your group project experiment method section is due in labs this weekExperimental designsSo far we’ve covered a lot of the details of experiments, now let’s consider some specific experimental designs.–1 Factor, two levels–1 Factor, multi-levels–Factorial (more than 1 factor)•(next Monday’s lecture)–Between & within factors•(this Wednesday’s lecture)Single variable – One Factor designs1 Factor, two levels–Basically you want to compare two treatments (conditions)–The statistics are pretty easy, a t-testT-test = Observed difference btwn conditionsDifference expected by chance1 factor - 2 levelsExample–How does anxiety level affect test performance?•Two groups take the same test–Grp1 (moderate anxiety group): 5 min lecture on the importance of good grades for success–Grp2 (low anxiety group): 5 min lecture on how good grades don’t matter, just trying is good enough1 factor - 2 levelsparticipantsLowModerateTestTestRandom AssignmentAnxietyDependent VariableSingle variable – one Factoranxietylowmoderate8060low moderatetest performanceanxietyOne factorTwo levelsSingle variable – one FactorAdvantages:–Is the independent variable worth studying?•If no effect, then usually don’t bother with a more complex design–Sometimes two levels is all you need•One theory predicts one pattern and another predicts a different patternSingle variable – one FactorDisadvantages:–“True” shape of the function is hard to see•interpolation and extrapolation are not a good ideaInterpolationlowmoderatetest performanceanxietyWhat happens within of the ranges that you test?Extrapolationlow moderatetest performanceanxietyWhat happens outside of the ranges that you test?high1 Factor - multilevel experimentsFor more complex theories you will typically need more complex designs (more than two levels of one IV)1 factor - more than two levels–Basically you want to compare more than two conditions–The statistics are a little more difficult, an ANOVA (analysis of variance)1 Factor - multilevel experimentsExample (same as before with one more group)–How does anxiety level affect test performance?•Three groups take the same test–Grp1 (moderate anxiety group): 5 min lecture on the importance of good grades for success–Grp2 (low anxiety group): 5 min lecture on how good grades don’t matter, just trying is good enough–Grp3 (high anxiety group): 5 min lecture on how the students must pass this test to pass the course1 factor - 3 levelsparticipantsLowModerateTestTestRandom AssignmentAnxietyDependent VariableHighTest1 Factor - multilevel experimentsanxietylowmodhigh8060 60low modtest performanceanxietyhigh1 Factor - multilevel experimentsAdvantages–Gives a better picture of the relationship (function)–Generally, the more levels you have, the less you have to worry about your range of the independent variableRelationship between Anxiety and Performancelow moderatetest performanceanxiety2 levelshighlow modtest performanceanxiety3 levels1 Factor - multilevel experimentsDisadvantages–Needs more resources (participants and/or stimuli)–Requires more complex statistical analysis (analysis of variance and pair-wise comparisons)Pair-wise comparisonsThe ANOVA just tells you that not all of the groups are equal.If this is your conclusion (you get a “significant ANOVA”) then you should do further tests to see where the differences are–High vs. Low–High vs. Moderate–Low vs. ModerateNext timeAdding a wrinkle: between-groups versus within-groups factorsRead chapter