# Experimental Methods and Design 2

 Post-Hoc Comparisons. Most liberal/conservativce? Post-Hoc comparisons are comparisons run after data collection. Number of possible comparisons c = (a)*(a-1) with a=# of groups. To determine pairwise comparisons just divide by 2 Fisher’s LSD (very liberal) -> Modified Bonferroni-> Bonferroni-> Tukey’s HSD (very conservative) Familywise Error The probability of at least one Type I error (a) for a set of many comparisons. aFW = (c)(a) with c= # of comparisons “Fishing” Conducting a large number of statistical tests, without theoretical reasons, and then “fishing” out the significant test results. Calculating Fisher’s LSD Anything greater than Fisher's LSD is significant. T= t= A= a= AS= s= as= [T]= [A]= [AS]= T= Grand Totalt= # of grand totals (always 1)A= Total for each conditiona= # of levels for the IVAS= Individual scoress= # of participants per conditionas= Total # of participants[T]=T2/as[A]=(A12+A22)/s[AS]=AS2 Planned Comparisons Planned before the study is executed to test a specific hypothesis.Only difference in how they are conducted is the alpha level used to determine significance. Planned Comparisons: Rules for Creating Coefficients There must be 1 coefficient for each mean    – Means not included in the comparison have a coefficient of      zero There is always two sets of means being compared     – means in the same set have the same sign (+ or -) Coefficients must add to zero Orthogonality Orthogonal comparisons reflect independent or non-overlapping pieces of information.  The outcome of one comparison gives no indication whatsoever about the outcome of another orthogonal comparison. Non-orthogonal contrasts can be hard to interpret. What are the advantages of a Within-Subjects Design? Control of individual differences (aka subject differences)More likely to find an effectFewer participants neededEfficiency gains (less time-consuming and expensive)…  Sequence effects2) Carryover effectsa) Orderb) Practicec) Interferenced) Differential What confounds are specific to a Within-Subjects Design? Confounds are extraneous variables that vary in some non-random way across conditions1. Sequence:– People change as they spend time working on tasks – They can become bored, fatigued, or more excited.2. Carryover:– Responses to one condition influence the responses to a later condition.– Different from sequence effects. Not the passage of time, but the impact of one condition on another.2) Carryover effectsa) Orderb) Practicec) Interferenced) Differential AuthorArukio ID181616 Card SetExperimental Methods and Design 2 DescriptionNotes for experimental methods and design test 2 Updated2012-11-05T13:26:04Z Show Answers