Performance Bias By: Dr. Venkatesh Thiruganasambandamoorthy
Performance bias in this study refers to potential systematic differences in the care provided between groups other than the interventions of interest (point-of-care ultrasound). After enrolment, blinding (or masking) of physicians to the ultrasound results (specifically with regards to cardiac activity) might have reduced any bias introduced by the vigour of resuscitation which in itself affects outcomes. Hence, effective blinding would have ensured that the groups (with and without cardiac activity) received similar amount of attention and treatment.
Large population cohort studies are really the only method available for searching for associations between drugs and rare but serious adverse effects. Because there are so many potential confounders, high quality studies will attempt to adjust for these – propensity score matching is one method of confounder adjustment. Propensity score matching involves calculating conditional probabilities of having a certain outcome given the presence of pre-selected covariates (e.g. risk factors for a given outcome) and matching exposed and control subjects with similar propensity scores.
The critical reader will be wary of overstated conclusions in a research abstract. Be sure to examine the results presented and ask yourself if the conclusions are truly supported by the methods described and the data presented. The same applies when writing a research abstract –ensure that your conclusions follow directly from the data you describe and are realistic given your chosen methods.
Large databases provide a wealth of data to help answer questions which may never be answered with an expensive RCT. A key step, however, in database research is evaluating the accuracy of data entry and reassuring the reader that the data are high quality. This can be done by hand verifying a random sample of entries or re-verifying diagnostic codes, for example.
STROBE Statement By: Dr. Lisa Calder April 2012
Study Setting and Subjects By: Dr. Ian Stiell September 2012