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Table 7 Examples of curious supporting explanations for attrition bias judgments that may not appear to be suitable for judging this risk of bias domain

From: Assessments of attrition bias in Cochrane systematic reviews are highly inconsistent and thus hindering trial comparability

Study number Support for judgment Judgment for risk of attrition bias
82 Chinese article - unable to ascertain Unclear
144 This study was a feasibility study. Only 1 woman received the intervention. This study contributed no data to the review. Unclear
255 No pre-published protocol identified High or unclear
256 If we assume a person works for 40 h per week, then for 28 participants the working hours will be 8960 h for 8 weeks (4 weeks intervention and 4 weeks control period). However the study reported only 7729 working hours based on accelerometer data High
376 This is not clear from the paper. Author contacted, but when he moved jobs, the data files for this study were deleted Unclear
490 137 minus 28 equals 109, not 108 Unclear
492 Exact time periods of ‘before and after’ accident data were unclear. Authors reported that they “should be 3 to 5 years”. Unclear
494 1 - A reasonable account of how attrition was dealt with is given, but no specific reference to CONSORT Low
517 Documented evidence that the CONSORT guidelines have been followed Low
606 Data sparse largely narrative style Unclear
699 Numbers do not always add up - query if N for outcomes are based on those who answered specific questions on follow-up? High
727 Data of drop-outs was censored. Low
730 Eleven patients were withdrawn before random assignment: 1 declined further participation, 8 were withdrawn by their physician, and 2 did not meet the entry criteria Low
744 Publication is in German and our translation is incomplete. Unclear
835 Differences in baseline characteristics of questionnaire responders vs non-responders (western ethnicity in 81% vs 54%, mean age 31 vs 28 years, median blood loss 1500 vs 1150 mL). Big difference in compliance to allocated treatment: 8 vs 34. The design of this trial carries a high risk for selecting the study population High
838 Primary and secondary endpoints not specified directly but do address aims Low
849 “The situations to consider eliminating the subject from data analysis did not arise” Low
850 No Table 1 to clearly describe participant characteristics. High
854 Duration of study not defined High
854 Criteria for kidney disease not defined Unclear
873 Denominators inconsistent in study Unclear