• Susanna Lehtimaki

COVID and back to school

This COVID-19 School and Community resource library is one of the most comprehensive attempts to summarize the evidence we have seen in the public domain on a range of issues related to COVID, kids and schools. It was updated just last week as was this WHO publication, summarized in a simple Q&A.

Please note that there is a still an “interpretation” made by the authors on the synthesis of evidence. Most of the articles they include are from peer reviewed journals (e.g. Lancet, JAMA). Those that are not are clearly marked as “lay articles” which as you know are less rigorous in terms of methods and more subject to bias. So best to focus on those from peer reviewed journals if you are going to “dig deep” into any of the topics. Also, for those of you working more internationally, you will note a focus on the US/Massachusetts (and a still somewhat conservative interpretation of some of the evidence).

Also, as I wrote previously, interpretation of evidence is complicated. When we read an individual study – first we review the methods and also the inferences or conclusions drawn. Peer review is one step in the process – but to derive real evidence we need to look at multiple studies, and in particular if an article reports on an observational study (vs a randomized trial where there is a matched control group).   

It is highly unusual to base national or state policy on one study. If there is limited evidence – we would start with a literature review. Within that, depending on the type of studies, we may grade the evidence. Here is an example of how strength of evidence is graded.

If there are enough studies, we can do a systematic review or meta-analysis which brings together findings from multiple studies and is considered the strongest type of review. While individual studies are helpful, they are never definitive, particularly if the study design is not a robust randomized controlled trial (which always has a comparison group).


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