Bias is defined as any tendency which prevents unprejudiced consideration of a question (Dictionary.com). Bias can occur at any phase of research, including study design, data collection, data analysis and publication thereby impacting on the validity and reliability of study findings. It is often difficult for the reader of a paper to fully understand if bias is or is not present, arguably there is always an element of bias in any study, readers must consider how bias might influence a study's conclusions (Gerhard, 2008). Critical appraisal of all studies will assist the reader in understanding risk of bias through for example, evaluating the strength of internal and external validity, and consideration of how the sample was selected, the study design, if the sample size was adequate, choice of outcome measures, how randomisation was achieved (if appropriate), if the study was blinded, attrition and publication bias. All publications should, as a course of best practice, state their source of funding.