Letters to the Editor RE: ‘‘BIAS IN CLINICAL INTERVENTION RESEARCH’’

In her Journal review discussing the potential biases of controlled trials, Gluud stated that ‘‘[t]he purpose of blind-ing is to prevent bias associated with patients ’ and investi-gators ’ expectations. If interventions are compared with no intervention, an identical placebo may be used. The com-pared interventions must be identical in taste, smell, appear-ance, and mode of administration. Any difference may destroy the blinding’ ’ (1, p. 496). The last sentence of this quotation was based on three references, two of them focusing on vitamin C and common cold trials (2, 3). However, the Karlowski et al. trial (2) and the Chalmers review (3) were both shown to be erroneous a decade ago (4–6). For example, Karlowski et al. did not mention that 42 percent of the recorded common cold epi-sodes were missing from their subgroup analysis that wa