Quality appraisal cohort studies (National Institutes of Health critical appraisal tool)
| First author and date (listed in chronological, then alphabetical order) | Was the research question or objective in this paper clearly stated? | Was the study population clearly specified and defined? | Was the participation rate of eligible persons at least 50%? | Were all the subjects selected or recruited from the same or similar populations? | Was a sample size justification, power description or variance and effect estimates provided? | For the analyses in this paper, were the exposure(s) of interest measured prior to the outcome(s) being measured? | Was the timeframe sufficient so that one could reasonably expect to see an association between exposure and outcome if it existed? | For exposures that can vary in amount or level, did the study examine different levels of the exposure as related to the outcome? | Were exposure measures (independent variables) clearly defined, valid, reliable and implemented consistently across all study participants? | Was the exposure(s) assessed more than once over time? | Were the outcome measures (dependent variables) clearly defined, valid, reliable, and implemented consistently across all study participants? | Were the outcome assessors blinded to the exposure status of participants? | Was loss to follow-up after baseline 20% or less? | Were key potential confounding variables measured and adjusted statistically for their impact on the relationship between exposure(s) and outcome(s)? | Overall rating of study quality for determining cause and effect relationship |
| Buor 200421 | Y | Y | N | N | N | N | N | Y | N | NA | N | NR | NA | N | Poor |
| McCray 200422 | N | Y | N | Y | N | N | Y | Y | CD | N | N | N | NA | Y | Fair |
| Foggin 200623 | Y | Y | N | N | N | N | N | N | Y | NA | N | N | NA | N | Poor |
| Gibson 200624 | Y | Y | NR | N | N | Y | Y | N | Y | N | Y | NR | NR | N | Fair |
| Rao, 200625 | Y | Y | N | CD | N | N | N | Y | N | NA | N | N | NA | N | Poor |
| Hemson 200726 | N | Y | CD | CD | N | N | N | Y | N | NA | N | N | NA | N | Poor |
| BeLue 200827 | Y | Y | CD | Y | N | N | Y | Y | N | NA | CD | CD | NA | N | Poor |
| Borah 201028 | N | Y | NR | Y | N | N | N | N | N | N | N | N | NA | N | Poor |
| Geere 201046 | Y | Y | N | Y | N | N | N | Y | Y | NA | N | N | NA | N | Poor |
| Rauniyar 201129 | Y | Y | N | Y | N | N | N | N | N | N | N | CD | NA | Y | Poor |
| Devoto 201230 | N | Y | Y | Y | Y | Y | Y | Y | N | Y | N | Y | Y | Y | Good |
| Singh 201233 | Y | Y | CD | N | N | N | N | N | N | NA | N | CD | NA | N | Poor |
| Stevenson 201234 | Y | Y | NR | Y | N | N | N | N | N | N | N | NR | NR | Y | Poor |
| Yallew, 201235 | Y | Y | N | Y | N | N | N | Y | Y | NA | N | N | NA | N | Poor |
| Asaba 201331 | N | Y | N | Y | N | N | N | N | N | N | N | N | NA | N | Poor |
| Robson 201332 | Y | Y | CD | N | Y | N | N | Y | Y | NA | N | N | NA | N | Poor |
| Henley 201436 | Y | Y | N | N | N | N | N | N | N | NA | Y | NR | NA | Y | Fair |
| Mugambe 201437 | Y | Y | N | Y | Y | N | N | Y | N | NA | N | N | NA | Y | Fair |
| Ono 201438 | y | y | CD | y | N | N | N | Y | N | NA | Y | N | NA | Y | Fair |
| Berrian 201639 | Y | Y | Y | Y | Y | N | N | Y | N | NA | N | NR | NA | N | Poor |
| Cook 201640 | Y | Y | CD | Y | N | N | N | Y | CD | NA | N | CD | NA | N | Poor |
| Hennegan 201645 | Y | Y | N | Y | N | N | Y | NA | Y | Y | N | N | Y | N | Poor |
| Krumdieck 201641 | Y | Y | Y | Y | N | N | N | N | N | NA | N | NR | NA | N | Poor |
| Dapaah 201742 | Y | Y | N | Y | N | N | N | N | N | NA | N | N | NA | N | Poor |
| Geere 201843 | Y | Y | Y | N | Y | N | CD | Y | N | NA | Y | Y | NA | Y | Fair |
| Thomas 201844 | Y | Y | N | Y | N | N | N | Y | N | N | N | N | NA | Y | Poor |
CD, cannot determine; N, no; NA, not applicable; NR, not reported; Y, yes.