The Limits of the External Validity of the Effects of Each

Multiple Choice

The limits of the external validity of the effects of each of the two independent variables in a complex design are specified when

A) there is no interaction effect of the two variables and neither variable produces a main effect.
B) there is no interaction effect of the two variables but significant main effects for both variables.
C) there is no interaction effect of the two variables and one independent variable has a main effect but the other variable does not.
D) there is an interaction effect of the two variables and main effects of the variables may or may not be present.