(Scenario II) Suppose the Vendor Who Sold the Rats to the Researchers

(Scenario II) Suppose the vendor who sold the rats to the researchers in Scenario II only had 20 rats left. The researchers needed a total of 40 rats to conduct this study, so they buy the remaining 20 from another vendor. The strain and sex of the rats from both vendors are identical, but the age of the rats from one vendor is older than the rats from the second vendor. Which of the following is a potential problem for this study?

A) Changes in vasculature may be due to the age of the rat, and not the treatment it was exposed to.
B) The small sample size makes it impossible to establish internal validity.
C) The study is confounded because vendor type is an uncontrolled variable.
D) There are no potential problems because the researchers ensured that all rats were randomly assigned to the treatment conditions.