—We agree with Radvanović et al that the choice of a reference group is of critical importance in epidemiologic studies such as the one we reported in 19831 and the one more recently published by Cvetković et al.2 In choosing a reference group with which to compare survival of persons who have undergone cataract extracton, we recognized that the hypothesis of interest to us was that "cataracts result from systemic processes that are associated with aging" and that such an association should be reflected in survival. To test that hypothesis, "we searched for a reference group that would provide comparability in factors influencing mortality" to avoid selection biases. Comparison with the general population was considered inadequate because persons undergoing cataract extraction at the New England Medical Center, Boston, are likely to differ from that potential comparison group in a number of ways that are expected to influence
Hirsch RP, Schwartz B. Survival of Patients With Cataract-Reply. Arch Ophthalmol. 1987;105(2):166–167. doi:10.1001/archopht.1987.01060020020004
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