PowerPoint presentation to accompany Research Design Explained 6th edition ; ©2007 Mark Mitchell & Janina Jolley Chapter 12 Factorial Designs

PowerPoint presentation to accompany Research Design Explained 5th edition ; ©2004 Mark Mitchell & Janina Jolley The 2X2 Factorial Design l The two by two yields four (two pairs of) simple main effects l Averaging a treatment’s main effects lets you find the overall main effect: The average effect of varying a factor l Comparing a factor’s simple main effects lets you find the interaction between two factors

PowerPoint presentation to accompany Research Design Explained 5th edition ; ©2004 Mark Mitchell & Janina Jolley Interactions Are Important: l Interesting questions in modern psychology are often questions about interactions l External validity questions are questions involving interactions l Questions in applied psychology are often questions involving interactions

PowerPoint presentation to accompany Research Design Explained 5th edition ; ©2004 Mark Mitchell & Janina Jolley Potential Results of a 2X2 Factorial Experiment l A main effect and no interaction l Two main effects and no interaction l Two main effects and An interaction l Interaction without main effects l One main effect and An interaction l No main effects and no interaction

PowerPoint presentation to accompany Research Design Explained 5th edition ; ©2004 Mark Mitchell & Janina Jolley The Mathematics behind an ANOVA table l SS effect / df effect = MS for effect l df for main effect = Levels of main effect -1 l df for interaction between two variables = df for 1st main effect X df for 2nd main effect l df for error term = Number of participants - total number of groups l MS effect / MS error = F l The larger F, the more likely the result is to be significant.

PowerPoint presentation to accompany Research Design Explained 5th edition ; ©2004 Mark Mitchell & Janina Jolley Interpreting the Results of a 2 X 2 Experiment l Main effects without interactions: It all adds Up l Interactions: When combining factors leads to effects that appear to differ from the sum of the individual effects

PowerPoint presentation to accompany Research Design Explained 5th edition ; ©2004 Mark Mitchell & Janina Jolley Putting the 2X2 to Work l Adding a replication factor to increase generalizability l Using an interaction to find an exception to the rule: Looking at a potential moderating factor

PowerPoint presentation to accompany Research Design Explained 5th edition ; ©2004 Mark Mitchell & Janina Jolley The Hybrid Design: A Factorial Design that Allows You to Study Non-Experimental Variables l Limitation: Can’t make causal statements about the nonexperimental factor l Advantages –Increasing generalizability –Studying effects of similarity –Finding an exception to the rule

PowerPoint presentation to accompany Research Design Explained 5th edition ; ©2004 Mark Mitchell & Janina Jolley Concluding Remarks l Factorial experiments allow you to –Look at the effects of more than one factor at a time –Look for interactions, so that you can l Find moderating variables l Look at the effects of similarity l Answer more interesting questions