The researcher is studying an intervention designed to reduce job stress in emergency department ...

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Rationale 1: Selection threat should be considered in experimental studies when subjects are not randomly assigned to the experimental and comparison groups. There is no evidence that this is the case in this study.
Rationale 2: The threat of history occurs when some event besides the experimental treatment occurs during the course of a study, and that event influences the dependent variable. In this case, the death of an emergency department nurse in the line of duty would likely be well covered in the media and would potentially impact the stress levels of ED nurses.
Rationale 3: The testing threat may occur in studies where a pretest is given or where subjects have knowledge of baseline data. Subjects may remember the answers given on the pretest and put the same answers on the posttest. There is no evidence that this is the case in this study.
Rationale 4: Maturation becomes a threat when changes, such as becoming older or taller, occur within the subjects during the experiment and those events influence the study results. There is no evidence that this is the case in this study.