title: Diminishing seasonality of self-harm: Temporal trends in Hong Kong SAR.
abstract: The study of temporal variation in self-harm is important to understanding the underlying mechanisms of its occurrence. There are fewer studies on temporal variation in self-harm than in suicide. The aim of this study was to examine the seasonality of self-harm in Hong Kong and to test the hypothesis of diminishing seasonality.
  
  
  
  We used secondary data from medical records of self-harm obtained from all the public hospitals in Hong Kong under the management of the Hospital Authority. We identified 59,473 distinct episodes involving 36,411 patients. From these, monthly statistics of self-harm from January 2002 to December 2011 were calculated. Harmonic analysis was conducted to examine the presence and magnitude of seasonality.
  
  
  
  A bi-seasonal pattern alongside a stronger one-cycle pattern from 2002 to 2006 was identified. During the period 1997-2001, this contracted to a one-cycle pattern with a peak in summer (May to July) and a nadir in winter (December). The magnitude of seasonality diminished greatly, as shown by harmonic analysis. The extent of diminishing seasonality was larger among women and people under 55 years old.
  
  
  
  The study covered only self-harm patients who had visited a hospital. Cases which required no medical attention and those where the patient consulted private doctors could not be included, indicating bias towards more severe cases of injury and poisoning.
  
  
  
  This study provides some evidence of diminishing and even vanishing seasonality of self-harm in Hong Kong, a phenomenon mainly found in younger individuals. It could be related to the increasing use of social media to connect people, especially the younger generation. The impact of seasonal events and activities, as in the past, has become less significant in the social media era.
authors.affiliation: Centre for Suicide Research and Prevention, The University of Hong Kong, Hong Kong.
authors.forename: Chi-Leung
authors.initials: CL
authors.lastname: Kwok
authors.affiliation: Centre for Suicide Research and Prevention, The University of Hong Kong, Hong Kong; Department of Social Work and Social Administration, The University of Hong Kong, Hong Kong. Electronic address: sfpyip@hku.hk.
authors.forename: Paul S F
authors.initials: PSF
authors.lastname: Yip
mesh_terms: D000293:Adolescent; D000328:Adult; D000367:Age Factors; D000368:Aged; D002648:Child; D005260:Female; D006723:Hong Kong / Q000453:epidemiology; D006801:Humans; D008297:Male; D008875:Middle Aged; D012621:Seasons; D016728:Self-Injurious Behavior / Q000453:epidemiology*; D013405:Suicide / Q000706:statistics & numerical data*; D013406:Suicide, Attempted / Q000706:statistics & numerical data*; D055815:Young Adult
keywords: Diminishing seasonality; Hong Kong; Seasonal variation; Self-harm; Suicide