# Announcements 1/13/02

Introduction To Complex Designs Outline of Todays Discussion 1. Introduction to Complex Designs 2. Analysis of Complex Designs Part 1 Introduction To Complex Designs Intro To Complex Designs

1. According to our text, what is a complex design? 2. Potential Pop Quiz Question: What is a synonym for complex design? 3. Potential Pop Quiz Question: What is the simplest

complex design? 4. Potential Pop Quiz Question: Explain the primary advantage associated with complex designs? Intro To Complex Designs 1. Lets get some practice reading graphs.

2. Some of the following graphs are from complex designs, and some are not. 3. In addition to describing each graph, indicate whether (and why) the design is simple or complex Intro To Complex Designs

Describe how the variables are plotted in this graph. How many levels does the IV have, and what are they? Intro To Complex Designs Describe how the variables are plotted in this graph. How many IVs, and how many levels of each? Intro To Complex Designs Describe how the variables are plotted in this graph. How many IVs, and how many levels of each?

Intro To Complex Designs Heres an oldie but goodie Which graph is messed up? Part 2 Analysis of Complex Designs Analysis of Complex Designs 1.

In this section, well focus on three concepts, main effects, interactions, and simple effects. 2. Well consider each in turn 3. Main Effect - The overall effect of one independent variable in a complex design.

4. A main effect of one IV is assessed by collapsing across (averaging over) all levels of the other IV. Analysis of Complex Designs 1. When we consider main effects, we temporarily simplify the research design. 2.

For example, in an AxB design (read, A by B), we might have 2 levels of factor A, and 3 levels of factor B. 3. When we consider the main effect of factor A, factor B goes away temporarily, and were back to a simple design with one factor that has 2 levels. 4.

When we consider the main effect of factor B, factor A goes away temporarily, and were back to a simple design with one factor that has 3 levels. Analysis of Complex Designs Would someone try to describe the main effect of training (i.e., factor A) here? Analysis of Complex Designs Would someone try to describe the main effect

of task (i.e., factor B) here? Analysis of Complex Designs 1. Now, lets develop some intuitions about interactions 2. Can someone think of two chemicals that are harmless when alone, but lethal when they interact? This is only a mediocre analogy. Lets define it.

3. Interaction - the phenomenon that occurs when the effect of one IV depends on the level of a second IV. Analysis of Complex Designs 1. Good scientists can detect interactions using a couple of tricks. (Very sneaky).

2. The first trick requires looking for parallel lines (or at least parallel trends) in graphs. 3. If the lines or trends in a graph are parallel, then there is no interaction. 4.

To the extent (note the caution in to the extent) that lines or trends depart from parallel, there is an interaction Analysis of Complex Designs Is there an interaction here? Also, could someone describe the main effects? Analysis of Complex Designs How cool is this?

Analysis of Complex Designs Is there an interaction here? Also, could someone describe the main effects? Analysis of Complex Designs Is there a unique character here? Analysis of Complex Designs Is there a unique character here?

Analysis of Complex Designs From Shaughnessy, Zechmeister & Zechmeister Is there an interaction here? Also, could someone describe the main effects? Analysis of Complex Designs From Shaughnessy, Zechmeister & Zechmeister Is there an interaction here? Also, could someone describe the main effects?

Analysis of Complex Designs From Shaughnessy, Zechmeister & Zechmeister What is the dimensionality of this experiment? Is there an interaction here? Analysis of Complex Designs 1. A second trick requires a little more effort, and is less intuitivebut it still works

2. The subtraction method for finding interactions involves comparing the differences between the means in each row (or column) of a means-table. 3. To the extent (note the caution in to the extent) that the differences are different, there is evidence for an interaction.

Analysis of Complex Designs Is there an interaction here? Also, could someone describe the main effects? Analysis of Complex Designs Is there an interaction here? Also, could someone describe the main effects? Analysis of Complex Designs

1. Questions so far on interactions? 2. Lets now get just a little more complicated, and move to a complex design that has three independent variables. 3. Well consider the simplest 3-way design, i.e., a 2x2x2.

4. The first problem we encounter is that we draw graphs on 2-dimensional surfacesbut we have 3 dimensions of variability in our independent variables. 5. Any suggestions? Analysis of Complex Designs

From Shaughnessy, Zechmeister & Zechmeister Is there an interaction here? 3-Way Interaction Vertical Activity Vertical Activity Day 1 Sig 2-Way Interaction stress no stress

1400 1200 1200 1000 1000 800 600 400

800 600 400 200 200 0 0

drug saline drug treatment stress no stress 1400 vertical Activity vertical activity

Vertical Activity Day 2 No 2-Way Interaction drug saline drug treatment Denison Student Research on Cross-sensitization to Amphetamine By Mandy Calkins (2004) and Professor Susan Kennedy

Analysis of Complex Designs 1. For a 2-factor experiment (AxB), we can have a main effect of A, a main effect of B, and an AxB interaction. 2. For a 3-factor experiment (AxBxC), we can have a main effect for each of the variables, but many different interactions.

3. The interactions could be AxB, AxC, BxC, or AxBxC! Things get complicated quickly. :-) Analysis of Complex Designs 1. Lets return to a humble, AxB design and consider a few additional points about interactions. 2.

First, we should be careful about reporting interactions if we have reason to believe there may be floor or ceiling effects Analysis of Complex Designs From Shaughnessy, Zechmeister & Zechmeister In your own words, why is this interaction bogus? Analysis of Complex Designs

1. Also, it is good practice to look at main effects only after establishing that the interaction is non-significant. 2. In other words, a significant interaction can complicate the interpretation of main effects Analysis of Complex Designs

Probability of Finding Spouse Interactions Obscure Main Effects 0.8 0.6 0.4 0.2 0 Young

Old Male Female Gender Here, it could be misleading to say that there is no main effect of gender or age. The interaction can obscure a main effect. Analysis of Complex Designs

Probability of Finding Spouse Interactions Obscure Main Effects 0.8 0.6 0.4 0.2 0 Young

Old Male Female Gender Whats wrong with this graph? Analysis of Complex Designs Probability of Finding Spouse

Interactions Obscure Main Effects 0.8 0.6 0.4 0.2 0 Young Old Male

Female Gender Shaughnessy,JJ, Shaughnessy, EB, and Zechmesiter, JS. Research Methods Psychology, Hill. Whatsinwrong with McGraw this graph?

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