RESEARCH ARTICLE Similarity of patient chara n

Full list of author information is available at the end of the articleBackground Study methodology is paramount because it affects the quality of the data, hence the interpretation of results and future clinical implications. The duration of the study is an important variable which in stroke studies can be in-fluenced by case-mix and seasonal variations. Case-mix, the array of different disease and health problems treated [1], (in this case, stroke severity and age structure of pa-tients etc.) influences hospitals ’ performance which is of relevance to patients, clinicians, commissioners and ser-vice providers. For research studies such as clinical trials, case-mix match between intervention and controls is im-portant so that results are due to interventions studied and not due to observed differences in case-mix. Keeping the duration of data collection to a minimum is of interest because collecting data is time consuming, expensive and resource draining. The duration of data collection has relevance in conducting clinical audits where there are clinical implications for conducting audit cycles in a timely manner. Changes implemented after an initial audit should be evaluated quickly in order to determine if the changes should be abandoned o