Table 2

Potential threats to inference when examining data across cohorts
Threats Description
Contextual The specific contexts from which samples were derived and recruited may influence results.
Historical Events occurring between observations may influence results. May also relate to factors impacting on one cohort but not another at baseline assessments.
Time synchronicity Studies are not conducted at a similar point in time, allowing a potential for factors or events associated with the time of administration to influence results. The length of time between follow-up assessments may also differ.
Geographic region Similar to contextual factors, but specifically associated with features of geographical region.
Sampling frame and methods Sampling frame (who was recruited) and methods could influence results (e.g., survey vs. phone based responses, and methods of following up non-responders).
Measurement equivalence Measurement methods or characteristics may differ across cohorts or change differentially (e.g., for assessments to be comparable across samples and timepoints, we may need to examine participant responses and demonstrate that the same latent factors were assessed).

Allen et al.

Allen et al. BMC Medical Research Methodology 2013 13:122   doi:10.1186/1471-2288-13-122

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