Methodological issues arising from systematic reviews of the evidence of safety of vaccines

There was some disagreement among the articles whether the research question should be specific (narrowly formulated) or general (broadly formulated).

“There was some disagreement (Table 4) whether the research question should be specific (narrowly formulated) [51, 53], or general (broadly formulated) [35, 47, 49].”

About one third of the articles acknowledged that searching for observational studies requires additional time and resources because of lack of specific search filters and poorly established or inconsistently used indexing terms.

“About one third of the articles acknowledged that searching for observational studies requires additional time and resources because of lack of specific search filters and poorly established or inconsistently used indexing terms [38, 39, 47, 49, 56, 58, 59, 64, 65].”

Recommendations were made mainly on two topics: whether different study designs should be included in a systematic review; and whether different study designs should be analysed together in a single meta-analysis.

“Recommendations were made mainly on 2 topics: whether different study designs should be included in a systematic review; [29, 34, 37–39, 49, 56, 65, 73, 75] and whether different study designs should be analysed together in a single meta-analysis [8, 34, 35, 37, 38, 42, 49, 51, 56, 61, 70, 75–78].”

Twenty-five (27%) articles gave recommendations on item "considering different study designs", with publication dates between 1995 and 2016 (median year 2007).

“Twenty-five (27%) articles gave recommendations on item “considering different study designs” [8, 29, 34, 35, 37–39, 42, 44, 49, 51, 56, 61, 65, 70, 73, 75, 76, 77–83], with publication dates between 1995 and 2016 (median year of publication 2007).”

Most articles considered the combination of RCTs and non-randomised designs.

“Most articles considered the combination of RCTs and non-randomised designs [29, 35, 38, 39, 49, 51, 56, 61, 75, 81].”

The majority of articles advised against the use of scales but 12 articles recommended their use.

“The majority of articles advised against the use of scales but 12 articles recommended their use [29, 30, 48–50, 52, 53, 56, 66, 77, 86, 91].”

Twenty (22%) articles reported on item "publication bias", with publication dates between 1994 and 2012 (median year 2001).

“Twenty (22%) articles reported on item “publication bias” [16, 29, 33, 34, 36, 46, 48–50, 55, 56, 61, 70, 78, 85, 95–99], with publication dates between 1994 and 2012 (median year of publication 2001).”