Compensatory treatment , the subjects in the control group are often deprived of something considered to be of value. In such cases, there may be pressures to offer some type of compensation. Demoralization , on the other hand, feelings of deprivation among the control group may result in their giving up or not trying as hard at the posttest. Diffusion or imitation of treatment , it s possible that the experimental group will pass on some elements of the treatment to the control group. Expectancies of experimental staff.
Process analysis is used to study possible treatment misidentification problems.
The ability to generalize from a sample, or a subset, of a larger population to that population itself. Reactive or interaction effect of testing , in which a pretest might increase or decrease the respondent s sensitivity or responsiveness to the experimental variable and thus make the results obtained for a pretested population unrepresentative. The interaction effects of selection biases and the experimental variable . Reactive effects of experimental arrangements , which would preclude generalization about the effect of the experimental variable upon persons being exposed to it in nonexperimental settings. Multiple-treatment interference , likely to occur whenever multiple treatments are applied to the same respondents, because the effects of prior treatment are not usually erasable.