Question

PART 2: Practice with Experiments and Validity Concerns

Are people distracted by gory photographs? To find out, a researcher has participants work on a computer task in which a series of letters appears on a computer screen, one at a time; participants press the space bar when they see a vowel, and they do nothing when they see a consonant. Participants are supposed to respond as fast as they can to each letter. Participants do 10 practice trials first and then a block of 20 test trials. Just before the second trial, the experimenter flashes a cheerful photograph of a forest. Then, just before the eighteenth test trial, the experimenter flashes a gory photograph of an accident scene. He finds that people’s response time to the eighteenthtest trial is much slower than their response to the second test trial, and he concludes that gory photographs do distract people more than cheerful ones.

Does this study have any internal validity problems? If so, identify whether the problem is a design confound, a selection effect, or an order effect and explain why.

Explain clearly how the study might be changed so that it does not have the internal validity problem.

Answer 1

The internal validity of this design is weak, as the results in this design will the be the effect of faulty design rather than the independent variable. The specific problem this design has is order effects. Order effects mean that the independent variables which are placed in a certain order tend to generate a certain result. Here, the cheerful photograph is placed very early in the trail (2nd) and the gory images are placed very late (18th). So, there is a big difference in the order of these two variables. Till the 18th trail, fatigue and slowness can kick in as the person may get tired till the 18th trial, and because of this the reaction time may get slower, and not because of the independent variable itself. To correct this design, both these independent variable should be kept around each other and not to far away, so that order effects do not happen.