Estimating Incidence Rate of Hospital-Treated Self-Harm in Hong Kong Using Capture-Recapture Approach

A surveillance system for self-harm has not been established in Hong Kong. The existing data source has an unknown degree of underreporting, and therefore a capture-recapture method has been proposed to correct for the incompleteness.

To assess the underestimation of the incidence of self-harm cases presenting to hospital in Hong Kong using a capture and recapture method.

Two different yet overlapping hospital administrative datasets of self-harm were obtained from all public hospitals in Hong Kong. From 2002 to 2011, 59,473 distinct episodes involving 36,411 patients were identified. A capture-recapture model considering heterogeneous capture probabilities was applied to estimate the number of self-harm episodes.

The estimated number of self-harm incidence was 79,923, equally shared by females and males. Cases of self-harm by females were more likely to be ascertained than those by males. The estimated annual incidence rate of self-harm in Hong Kong from 2002 to 2011 ranged from 96.4 in 2010 to 132.7 in 2002.

The proposed method does not include patients who required no medical attention and those where the patient consulted private doctors.

The capture-recapture model is a useful method for adjusting the underestimation of self-harm cases from existing databases when surveillance system is not available and to reveal some hidden patterns.