Chapter 12 Factorial Designs Power Point presentation to

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Chapter 12 Factorial Designs Power. Point presentation to accompany Research Design Explained 6 th

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

The 2 X 2 Factorial Design l l l The two by two yields

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

Interactions Are Important: l l l Interesting questions in modern psychology are often questions

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

Potential Results of a 2 X 2 Factorial Experiment l l l A main

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

The Mathematics behind an ANOVA table l l l SS effect / df effect

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

Interpreting the Results of a 2 X 2 Experiment l l Main effects without

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

Putting the 2 X 2 to Work l l Adding a replication factor to

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

The Hybrid Design: A Factorial Design that Allows You to Study Non-Experimental Variables l

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

Concluding Remarks l Factorial experiments allow you to – Look at the effects of

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 l l Find moderating variables Look at the effects of similarity Answer more interesting questions *Power. Point presentation to accompany Research Design Explained © 2004 Mark Mitchell & Janina Jolley 5 th edition;

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