Introduction To Complex Designs

Introduction ToComplex Designs

Outline of Today’s Discussion • Introduction to Complex Designs • Analysis of Complex Designs

Part 1 Introduction To Complex Designs

Intro To Complex Designs • According to our text, what is a “complex design”? • Potential Pop Quiz Question: What is a synonym for “complex design”? • Potential Pop Quiz Question: What is the simplest complex design? • Potential Pop Quiz Question: Explain the primary advantage associated with complex designs?

Intro To Complex Designs • Let’s get some practice reading graphs. • Some of the following graphs are from complex designs, and some are not. • 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 IV’s, and how many levels of each?

Intro To Complex Designs Here’s an oldie but goodie… Which graph is “messed up”?

Part 2 Analysis of Complex Designs

Analysis of Complex Designs • In this section, we’ll focus on three concepts, main effects, interactions, and simple effects. • We’ll consider each in turn… • Main Effect - The overall effect of one independent variable in a complex design. • A main effect of one IV is assessed by “collapsing across” (averaging over) all levels of the other IV.

Analysis of Complex Designs • When we consider main effects, we temporarily simplify the research design. • For example, in an AxB design (read, “A by B”), we might have 2 levels of factor A, and 3 levels of factor B. • When we consider the main effect of factor A, factor B “goes away” temporarily, and we’re back to a simple design with one factor that has 2 levels. • When we consider the main effect of factor B, factor A “goes away” temporarily, and we’re 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 • Now, let’s develop some intuitions about interactions… • Can someone think of two chemicals that are harmless when alone, but lethal when they “interact”? This is only a mediocre analogy. Let’s define it. • Interaction- the phenomenon that occurs when the effect of one IV depends on the level of a second IV.

Analysis of Complex Designs • Good scientists can detect interactions using a couple of tricks. (Very sneaky). • The first trick requires looking for parallel lines (or at least parallel trends) in graphs. • If the lines or trends in a graph are parallel, then there is no interaction. • 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 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 What is the “dimensionality” of this experiment? Is there an interaction here?

Analysis of Complex Designs • A second trick requires a little more effort, and is less intuitive…but it still works… • The subtraction method for finding interactions involves comparing the differences between the means in each row (or column) of a means-table. • 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 • Questions so far on interactions? • Let’s now get just a little more complicated, and move to a complex design that has three independent variables. • We’ll consider the simplest 3-way design, i.e., a 2x2x2. • The first problem we encounter is that we draw graphs on 2-dimensional surfaces…but we have 3 dimensions of variability in our independent variables. • Any suggestions?

Analysis of Complex Designs From Shaughnessy, Zechmeister & Zechmeister Is there an interaction here?

Vertical Activity 3-Way Interaction Denison Student Research on Cross-sensitization to Amphetamine - By Mandy Calkins (2004) and Professor Susan Kennedy

Analysis of Complex Designs • For a 2-factor experiment (AxB), we can have a main effect of A, a main effect of B, and an AxB interaction. • For a 3-factor experiment (AxBxC), we can have a main effect for each of the variables, but many different interactions. • The interactions could be AxB, AxC, BxC, or AxBxC! Things get complicated quickly. :-)

Analysis of Complex Designs • Let’s return to a humble, AxB design and consider a few additional points about interactions. • 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 • Also, it is good practice to look at main effects only after establishing that the interaction is non-significant. • In other words, a significant interaction can complicate the interpretation of main effects…

Analysis of Complex Designs 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 What’s “wrong” with this graph?

Analysis of Complex Designs Shaughnessy,JJ, Shaughnessy, EB, and Zechmesiter, JS. Research Methods in Psychology, McGraw Hill. What’s “wrong” with this graph?

Introduction To Complex Designs