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Observational studies should carry a health warning
BMJ 2007; 334 doi: https://doi.org/10.1136/bmj.334.7586.179-c (Published 25 January 2007) Cite this as: BMJ 2007;334:179Observational studies have their place, although the results often depend crucially on the type of analysis used to generate them. A good illustration of this principle comes from a study comparing four different ways of looking at the effects of invasive …
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