Generalizability of a prediction rule for sick leave due to shoulder pain.

OBJECTIVES Recently, a rule was developed to predict sick leave related to shoulder pain during a period of 6 months after patients have consulted a general practitioner for a new episode of shoulder pain. The objective was to evaluate the generalizability of this prediction rule by testing it in two other populations of workers who had gone for a consultation in primary care for a new episode of shoulder pain. METHODS The prediction rule was derived in a prognostic cohort study (N=350). The outcome was sick leave related to shoulder pain during 6 months following the first consultation. The rule was tested on merged control groups from three trials on shoulder pain (N=128). In addition to this population, a recently conducted study on musculoskeletal disorders (N=224) was used to validate the prediction rule. The generalizability of the prediction rule was tested by studying calibration and discrimination in the validation cohorts. RESULTS The prediction rule showed reasonable calibration in both validation cohorts. The discriminative ability, with an area under the receiver operating characteristic (ROC) curve (AUC) of 0.70 in the derivation cohort was stable in the cohort of the musculoskeletal disorder study (AUC 0.71). In the control groups of the three randomized controlled trials of a Dutch shoulder study, the discriminative ability decreased to an AUC of 0.66. CONCLUSIONS The prediction rule for sick leave related to shoulder pain in a 6-month period following the first consultation in primary care showed adequate generalizability to another population of workers with shoulder pain participating in an observational cohort study. In the control groups of the three randomized controlled trials the prediction rule performed less well.