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Selection Bias vs. Surveillance Bias

It has been suggested that nurse practitioners may examine women who use oral contraceptives more often or more thoroughly than women who do not.

Question: If this is true, and if an association is observed between phlebitis and oral contraceptive use, the association may be due to _______________.

Answer: surveillance bias.

Why isn't "selection bias" the correct answer???

Solution This solution is FREE courtesy of BrainMass!

I think the rationale behind the answer is this: Assuming that there is not a true link between oral contraceptives and phlebitis, there is no reason why women going to the nurse practitioner with a complaint of phlebitis would be more likely than the population in general to be using oral contraceptives. Once a woman is at the nurse practitioner's office, there would be selection bias if the nurse chose to examine patients who had phlebitis and used oral contraception and those who had neither, but not those patients who only had one or the other.

Since the problem says that any bias on the nurses part is based on oral contraception use alone and not oral contraceptives and phlebitis, the answer is not selection bias. What the question is implying is happening is that nurses examine women who use oral contraceptives more thoroughly, and therefore identify more cases of phlebitis in that population than in the population of women who don't use oral contraceptives.