Contents

342 PART IV: Applied ResearchKEY CONCEPTSthreats to internal validity 315history 315maturation 315testing 316instrumentation 316regression 316subject attrition 317selection 317contamination 319novelty effects 319quasi-experiments 321nonequivalent controlgroup design 323simple interruptedtime-series design 332time series with nonequivalentcontrol group design 335program evaluation 336REVIEW QUESTIONS1 Identify two reasons why it might be especially important to carry out experimentsin natural settings.2 Explain how laboratory experiments and those in natural settings differ in control,external validity, goals, and consequences.3 Describe the three distinguishing characteristics of true experiments, and identifyhow the independent variable can be defined in terms of these characteristics.4 What obstacles do researchers have to overcome when they try to carry out experimentsin natural settings?5 Identify two procedures that permit researchers to assign participants randomly toconditions while still giving all participants access to the experimental treatment.6 Describe and explain the consequences of the three ways in which participants in acontrol group might respond when contamination occurs.7 Explain how novelty effects, including the Hawthorne effect, may influence aresearcher’s interpretation of the effectiveness of an experimental treatment.8 What do Cook and Campbell (1979) consider the best test of external validity?9 Explain why it is essential to use a pretest in the nonequivalent control groupdesign.10 Explain how one threat to internal validity is controlled in the nonequivalent controlgroup design, and describe a threat to internal validity that is not controlled in thisdesign.11 Identify two reasons why we cannot conclude that the treatment and control groupsin a nonequivalent control group design are equivalent even when the pretest scoresare the same for both groups.12 Explain the difference between a history threat to internal validity and what is calleda “local history effect” in the nonequivalent control group design.13 What is the major evidence for an effect of the treatment in a simple interruptedtime-series design, and what are the major threats to internal validity in thisdesign?14 Explain how the addition of a nonequivalent control group to a simple interruptedtime-series design reduces the threat to the internal validity of the design.15 Describe what type of information is being sought when evaluators ask each of thefour questions typically addressed in program evaluation.