10.5 OTHER THREATS TO INTERNAL VALIDITY OF BETWEEN-SUBJECTS DESIGNS
Remember that the goal of the between-subjects experimental design is to look for differences between groups on the dependent variable, and to demonstrate that the observed differences are caused by the different treatments (that is, by the manipulation of the independent variable ). If the different between the groups can be attributed to any factor other than the treatments, the research is confounded and the results cannot be interpreted without some ambiguity. Also recall from Chapter 6 that any factorthat allows for an alternative explanation for the research results is a threat to internal validity. Earlier in this chapter, we discussed the two major threats that can undermine the internal validity of a between-subjects study: assignment bias and confounding from environmental variables. Now, We consider additional potential confounds that are specifically related to between-subjects designs.