PPT Slide

Clarifying the causal status of “subject” variables through a

treatments x subjects design

Step 1: Develop a theory of the mechanism by which the subject variable

is assumed to determine behavior...for example, anxiety inhibits

task performance by distracting attention

Step 2: Select an independent variable that (a) can be experimentally

manipulated and (b) involves or influences the theoretical

mechanism that was postulated in Step 1...for example, presence

vs. absence of distracting stimuli in a task

Step 3: Carry out a Treatments x Subjects experiment in which the

treatments variable is the independent variable identified in

Step 2 (i.e., presence vs. absence of distracting stimuli) and the

subject variable is the variable whose causal status is at issue

(i.e., anxiety)

Step 4: The theory formulated in Step 1 predicts a significant interaction

between the treatment variable and the subject variable...for

example, anxiety should affect performance more on distracting

tasks than on non- distracting tasks. The presence of the

predicted interaction effect supports the view that the subject

variable really does affect (i.e., cause) behavior as theorized.