Other+sources+of+bias

What are other sources of bias?
toc Other sources of bias might include severe baseline imbalances, blocked randomization in unblinded trials (can lead to prediction of future assignments), or study design characteristics. Possible design-specific biases to look out for include having an inadequate wash-out period in a cross-over trial, or unit of analysis errors in cluster trials.

Tools

 * Guidance for minimizing bias in **cluster randomized trials** and **cross-over trials**: Cochrane Handbook, Chapter 16: Special Topics in Statistics


 * Analysis of cluster randomized trials:** One major difference in the analysis of a cluster randomized trial compared to a parallel randomized controlled trial is that the unit of analysis is no longer the individual participant, it is the group to which the participant belongs. This group, or cluster, could be something like a hospital, school, or community. Since the group is what has been randomized, the group is what must be analyzed. A simple summary of these concepts can be found here. Another consideration is that members of a group are likely more similar to each other than to members of other groups, therefore this correlation needs to be accounted for using the intracluster correlation coefficient (ICC).


 * Analysis of cross-over trials:** Since each participant in a cross-over trial will have two measurements, one for the effect of the intervention and one for the effect of the control, the appropriate analysis is a paired t-test.

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Examples
On this page we've compiled a number of examples of risk of bias assessments - the good, the bad, and those that are a bit unclear. Feel free to work through them yourself and come up with an assessment of **low **, **unclear ** , or **high ** risk of bias (our judgments and rationale are on the assessments page ), or download a spreadsheet file with the same information. RoB assessments are divided up into the seven major domains: sequence generation, allocation concelment, blinding of participants/personnel, blinding of outcome assessors, incomplete outcome data, selective outcome reporting, and other sources of bias. A quotation is given with the article title following in brackets.

If you have other examples, please add them to the list!

Risk of Bias Guidelines

Download examples:

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 * AOM: acute otitis media; RAD: reactive airway disease; full citation: Continuous twice daily or once daily amoxicillin prophylaxis compared with placebo for children with recurrent acute otitis media

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