A scientist is trying to determine whether the use of hair dye contributes to brain cancer. For his study, he compares the medical records of subjects that have been diagnosed with brain cancer to the records of healthy subjects. What is the most significant weakness in this type of study?

Question

anonymous · Answer

The test groups must be unusually large to generate significant data.
		This type of study is expensive and the data is difficult to analyze.
		This type of study must rely on medical records, which are often inaccurate or incomplete.
		The relationship between the hair dye and the cancer is difficult to determine.

anonymous · Answer

I think its C

blues · Answer

I agree. The medical records contain no info about whether or not the people used hair dye, so they would not be of any use in figuring out if hair dye affects brain cancer.