Dear Sir,

We read the paper by Panman et al. entitled “Predictors of unsuccessful pessary fitting in women with prolapse: a cross-sectional study in general practice” [1]. This study was performed to generate hypotheses about independent risk factors for unsuccessful pessary fitting in general practice. It was concluded that the variables lower patient age, higher body mass index (BMI) and underactive or inactive pelvic floor muscles are factors predicting unsuccessful pessary fitting in general practice [1]. However, although this was a valuable investigation and its findings are very interesting, some methodological issues should be considered.

First, the study by Panman et al. [1] evaluated predictors of unsuccessful pessary fitting in women with prolapse in a cross-sectional study, whereas longitudinal studies are more appropriate for making assumptions for clinical prediction models [2]. In other words, the temporality assumption (the dependent variable responds to changes in the independent variable) must be ensured in the prediction model. Thus, prediction models resulting from cross-sectional designs can be misleading [2, 3].

Second, considering the variables patient age, higher BMI and underactive or inactive pelvic floor muscles as independent predictors of unsuccessful pessary fitting in women with prolapse are an optimistic interpretation. The internal and external validation of the prediction model must be done through bootstrapping and split validation, respectively [4].

Therefore, the results of this study should be interpreted with consideration of the points discussed above.