Background: Because of specific methodological difficulties in conducting randomized trials, surgical research remains dependent predominantly on observational or non-randomized studies. Few validated instruments are available to determine the methodological quality of such studies either from the reader's perspective or for the purpose of meta-analysis. The aim of the present study was to develop and validate such an instrument. Methods: After an initial conceptualization phase of a methodological index for non-randomized studies (MINORS), a list of 12 potential items was sent to 100 experts from different surgical specialities for evaluation and was also assessed by 10 clinical methodologists. Subsequent testing involved the assessment of inter-reviewer agreement, test-retest reliability at 2 months, internal consistency reliability and external validity. Results:The final version of MINORS contained 12 items, the first eight being specifically for non-comparative studies. Reliability was established on the basis of good inter-reviewer agreement, high test-retest reliability by the κ -coefficient and good internal consistency by a high Cronbach's α -coefficient. External validity was established in terms of the ability of MINORS to identify excellent trials. Conclusions: MINORS is a valid instrument designed to assess the methodological quality of non-randomized surgical studies, whether comparative or non-comparative. The next step will be to determine its external validity when used in a large number of studies and to compare it with other existing instruments.Key words: comparative study, methodology index, non-randomized study.Abbreviation : MINORS, methodological index for non-randomized studies. INTRODUCTIONAlthough surgeons are now conducting an increasing number of randomized trials, 1 most of the available evidence in surgery comes from non-randomized studies, both comparative and noncomparative. Indeed surgical research remains an example of a situation where randomization is not always possible or feasible. 2 Beyond large randomized trials, systematic reviews are an important way to answer questions in surgery. However, the systematic review or meta-analysis of studies other than randomized trials may be difficult because combining the results of observational studies of heterogeneous quality could be highly biased.Observational studies include comparative studies such as case-control and cohort designs, and patient series which may or may not involve comparisons between two or more groups.Several papers have discussed the methodology of metaanalyses of observational studies 3,4 and checklists have been proposed but not formally validated. 5 Downs and Black used clinimetric criteria to develop a checklist which was applicable to both randomized and non-randomized studies without distinction. 6 The aim of the present study was to develop and validate a methodological index for non-randomized studies (MINORS) which could be used by readers, manuscript reviewers or journal editors to assess the quality...

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