Subgroup analysis of large trials can guide further research: a case study of vitamin E and pneumonia.

Previously, we hypothesized that the marginally significant 14% increase in pneumonia risk among those ATBC participants who started smoking at an early age (n = 21,657; the four lowest cells in Table 1 ) might correspond to a more unambiguous harmful effect among low-weight participants, based on an assumption of dose-dependency. 14 Then we found that vitamin E increased pneumonia risk in participants weighing less than 60 kg.

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