I am conducting a systematic review for my MPH and plan to synthesise the included papers following the SWiM guidelines. One of the possible standardised measures to use is 'effect direction'. However, the literature on the topic only mentions synthesis of evidence from interventions. I was wondering if I can use effect direction with evidence from an exposure (mostly cross-sectional, if that makes any difference). I know I won't be able to prove causality, but has anyone seen an example of effect direction applied to the evidence of an exposure rather than an intervention?

Reference:

Article Synthesis without meta-analysis (SWiM) in systematic reviews...