A researcher recruits 1,000 volunteers to participate in a health
study. The participants are randomly assigned to two groups, one
receiving the new drug, the other receiving the placebo. The subjects
are allowed to maintain their daily routines during the study except
the treatment (or placebo). The result shows that the recovery rate in
the treatment group is significantly higher than that of the control
group (p<.01). Which of the following is most likely threatened? A)
Internal Validity  B) Ecological Validity C) Reliability D)
Generalizability

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Clarification of Question by researchneeded-ga on 22 Jul 2004 10:08 PDT

Please give a very brief explanation of the answer.