Selective reporting involves investigators only reporting the most favourable results when they publish a trial, instead of reporting the results for all ABT-199 solubility dmso the outcomes that were measured. Reporting only favourable outcomes can create a misleading appearance of the effect of a therapy in the published literature. For example, imagine that a completely ineffective intervention is tested across several trials and each trial measures multiple outcomes. Most outcomes will show no significant

effect of the intervention. However, occasionally an outcome will show significant benefit or harm simply by chance. If the researchers publish the positive outcomes but not all of the non-significant and negative outcomes, readers could interpret falsely that the intervention is beneficial. A similar problem could occur when outcomes GSK2656157 mouse are analysed at multiple time points. Researchers may report that an intervention improves walking speed at 6 months, but fail to mention that it does not improve walking speed at 1, 2, 3, 9, 12 and 24 months. Prospective registration of clinical trials combats this problem in several ways. Journal editors and reviewers can compare the range of outcomes reported

in a manuscript against those listed in the registered protocol, requesting that any discrepancies be resolved by following the protocol. Readers can also compare the outcomes in the registered protocol against those in the published report, taking greater reassurance when they are consistent. Publication bias arises when trials with positive results are more likely to be published than trials with non-significant or negative results. Like selective reporting, this can also spuriously inflate the apparent effect of an intervention across the published data. For

example, a trial in which the intervention appeared to be effective may be published, while the three other trials in which the intervention appeared out ineffective or harmful languish in the filing cabinets of the investigators. If a trial is registered but never published, authors of a systematic review can still find the trial on the register and contact the authors to request the unpublished data for inclusion in the review. Therefore, prospective registration of clinical trials could further limit bias affecting the body of evidence that is available in published physiotherapy trials. Prospective clinical trial registration encourages transparency (Sim et al 2006) and may also make it more difficult for fraudulent authors to fabricate data. For example, some journals now ask for individual patient data to be provided routinely for checking (Herbert 2008) or audit data when fraud is suspected (Smith & Godlee 2005). Data collection should have occurred during the dates of data collection defined on the registry.