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date: 27 February 2021

Controls, Negative 

A Dictionary of Epidemiology

Miquel Porta

Precautionary procedures taken to detect possible sources of spurious associations. A study thus includes conditions under which it is expected to produce a null result, and researchers verify whether it does. In experiments, procedures include leaving out an essential agent, inactivating the hypothesized active agent or using an inert substance; in observational and experimental studies, checking for an effect impossible by the hypothesized mechanism (based on subject matter knowledge). Associations can be assessed among subjects exposed to doses clearly too low to produce the effect: if such association is present, the validity of the design, information, or analytic strategy should be questioned. Another example is the inclusion in questionnaires of irrelevant variables (“probe variables”) to assess if recall bias might be responsible for the observed magnitude of the associations between self-reported exposures and an outcome. A negative control outcome is one that cannot be affected by the exposure; e.g., mortality prior to influenza season for influenza vaccination. Similar to the ... ...

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