Rapid responses are electronic comments to the editor. They enable our users to debate issues raised in articles published on bmj.com. A rapid response is first posted online. If you need the URL (web address) of an individual response, simply click on the response headline and copy the URL from the browser window. A proportion of responses will, after editing, be published online and in the print journal as letters, which are indexed in PubMed. Rapid responses are not indexed in PubMed and they are not journal articles. The BMJ reserves the right to remove responses which are being wilfully misrepresented as published articles.
The problem of correlations between variables in a regression
equation might be stated more clearly. "Misleading" is an ambiguous term,
and could mean that the regression coefficient is biased. It could also
mean that the coefficient is imprecise or unreliable (as the answer
correctly implies). The standard errors of correlated variables grow as
their correlation increases. Statistical significance is lost. However,
this should be distinguished from "misleading" in the sense of biased