LAUSR

First, I would like to thank you for the opportunity to participate in this discussion aiming the growth of science and the assistance to physicians. The authors conducted a cross-sectional studywith the primary objective of assessing whether Asian ethnicity is a risk factor for the development of adhesive capsulitis.1 The study concludes that Asian ethnicity is an independent risk factor with an adjusted odds ratio (OR) of 3.6 (95% confidence interval [CI] of 2.0 to 6.5). However, this research was designed as an observational, cross-sectional study, which is inappropriate to answer this type of scientific question.2 A cross-sectional observational study is considered the gold standard for epidemiological studies aiming to reveal the precise prevalence of a particular issue with two or more associated variables; however, it is not the ideal study design to infer cause and effect.3 In prospective cohort studies, the researchers select a group of individuals and measure risk factors or exposures before the outcome, thus establishing temporality, an important factor in determining causality.3 This type of study is performed in some stages, including: sample selection, observation of each group over time, and comparison of groups exposed or not to the risk factor. Its main disadvantages are the high cost due to the large number of subjects that must be included in the study and the long follow-up time.3,4 Accordingly, the inference of the authors regarding the OR for Asian ethnicity and the development of adhesive capsulitismay be an overvaluedmeasure due to the study method and statistical analysis performed. Odds ratio is a statisticalmeasure used in longitudinal cohort studies, in which the incidence at the exposed group can be compared with the incidence at the nonexposed group, hence its name; as such, researchers should follow cases (Asian individuals) and controls (non-Asian individuals) over time to reach a possible risk factor.4