Most time-consuming disruptive factors were missing study results, incomplete case histories, and limited patient compliance.
The biggest threats to meta-analysis are publication bias due to missing studies with negative results and low-quality evidence due to methodological limitations imposed by included studies.
This may result in missing studies or retrieving many irrelevant documents.
The effect of publication bias was assessed using the 'Tim and Fill' procedure [ 11], by which the pooled OR and 95% CI are re-calculated after imputation of the results of hypothetically missing studies which would be needed to minimise the effect of publication bias.
However, in those reviews, only a single electronic database was searched resulting in some missed studies; there was no quality appraisal of current literature on this topic.
Implementation of the MRAF was limited at the beginning of the study resulting in missing data for some of the early participants.
There are several limitations to our study, including missing data resulting in exclusion of some participants, and lack of a control group.
The case study above removed participants with missing answers, resulting in a set of 430 participants.
For the present study, discrete genotypes were analysed and missing alleles resulting from imputation with findhap.
