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344 PART IV: Applied ResearchAnswer to Stretching Exercise1 History is a threat when an event other than the treatment can explain the participants’ improvement.For example, participants may have read self-help books, tried herbal supplements,talked to friends or pastors, or experienced any number of potentially beneficial “ treatments.”Any of these other events may have caused the depression to improve, rather than thepsychologist’s treatment.2 Maturation occurs when participants naturally change over time. One of the things we knowabout depression is that it tends to improve with time. Therefore, the participants’ improvementmay reflect natural decreases in depression over time, rather than the effect of the treatment.3 A testing threat occurs when a first administration of a test influences subsequent testing. In thisstudy, participants may have remembered their earlier responses on the depression measureand, perhaps in an effort to demonstrate they improved, chose responses that indicated lessdepression at posttest (even if they didn’t feel less depressed). An instrumentation threat occurswhen the measure used to assess thoughts, feelings, and behavior changes over time. Becausethe same questionnaire was used for both the pretest and posttest, this threat is less likely.4 Statistical regression is possible when participants are selected because they are extreme ona pretest measure. In this study, participants were selected because they were depressed—they scored high on a measure of depression. It’s possible that the lower scores at posttestindicated improvement because of statistical regression to the mean, not because of the effectsof treatment.Answer to Challenge Question 1A The nonequivalent control group design was used in this study.B Students may perceive random assignment to the two sections as unfair because they wouldnot have a choice about which section they would take. If we do not know whether multimediainstruction is effective, then random assignment is the best and fairest method todetermine whether multimedia instruction is effective.C If only the students who had received multimedia instruction had been tested, the design ofthe study would have been a single group pretest-posttest design. There are several threatsto the internal validity of a pretest-posttest single group design. That is why it is referred toas a pre-experimental design or a bad experiment. One possible threat in this study is dueto testing; that is, students often improve from an initial test in a course to the second testbecause they gain familiarity with the testing procedure and the instructor’s expectations.This improvement would be expected to occur even if multimedia instruction had not beenused. The nonequivalent control group design in this study controls for this threat becauseany increase in test scores due to testing effects would likely be the same for both groups. Agreater increase from the pretest to the posttest for the group given multimedia instruction,relative to the control group, can be interpreted as an effect of the instruction.