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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Eleven patients were withdrawn before random assignment: 1 declined further participation, 8 were withdrawn by their physician, and 2 did not meet the entry criteria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