Immediately after the intervention in an experimental study of the negative effects of smoking tobacco, the state tax on cigarettes increases the cost from $4 to $8 per pack. Which threat to internal validity does this pose?
a. Mortality
b. History
c. Testing
d. Selection
ANS: B
History is an event that is not related to the planned study but that occurs during the time of the study. History could influence a subject's response to the treatment and alter the outcome of the study. The attrition threat is due to subjects who drop out of a study before completion. The circumstances in which a study is conducted (history) influence the treatment and thus the generalizability of the findings. Sometimes, the effect being measured (testing) can be due to the number of times the subject's responses have been tested. The subject may remember earlier, inaccurate responses and modify them, thus altering the outcome of teh study.
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