Psychometric properties of the Chinese 15-item Patient Health Questionnaire in the general population of Hong Kong
Introduction
The 15-item Patient Health Questionnaire (PHQ-15) is an instrument for measuring somatic symptoms and screening for somatoform disorders. It is the somatization module of the full PHQ and asks people how bothersome 15 somatic symptoms are [1]. It includes 14 of the 15 most prevalent somatic symptoms of the Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition (DSM-IV), somatization disorder [1]. Those 15 somatic symptoms or symptom clusters account for more than 90% of the physical complaints encountered in primary care settings. Studies using the PHQ-15 in Western primary care samples confirmed that the somatic symptoms it captures were very common and exhibited a recognizable frequency profile and factorial pattern. Whether alone or in association with mental disorders, they were associated with significant functional impairment and predicted increased health care utilization [2], [3], [4]. Among the commonly known instruments for measuring somatization, items of the PHQ-15 overlap with other validated somatization screeners better than any other two screeners do with each other [1]. The PHQ-15 is also brief, giving it an advantage over lengthier somatization screeners (e.g., the 53-item Screening for Somatoform Symptoms [5] and the 37-item Somatic Symptom Inventory [6]) in time-limited research and clinical settings. It is perhaps not surprising that it has become the most widely used instrument for assessing somatic symptom severity and screening for somatoform disorders in recent years [1], [7], [8].
The above-mentioned strengths of the PHQ-15 notwithstanding, there are at least two areas where further research of the instrument is warranted. The first is about its psychometric characteristics in general population samples. Although somatic distress is likely to be a dimensional phenomenon in the community, studies using the PHQ-15 were usually based on clinical samples. This may partly be due to a general neglect of somatization and somatoform disorders in mainstream population-based epidemiological research. Nonetheless, the few Western general population studies that used the PHQ-15 to examine somatic symptom severity suggested that the instrument may be useful for community epidemiological research [9], [10], [11]. The second area is how well the PHQ-15 performs in non-Western settings. Historically, there has been a popular belief that Asians manifest a lower prevalence of mood and anxiety disorders than their Western counterparts because they are more prone to experiencing and/or manifesting distress in somatic terms [12], [13], [14]. This claim about “somatization” notwithstanding, there has been no population-based and cross-nationally comparable study of the distribution and severity of somatic symptoms in Chinese people. Among Chinese patients in both primary care and tertiary psychiatric services, somatic symptoms such as pains, insomnia and fatigue had been found to be common and associated with depressive and anxiety disorders [15]. Nonetheless, although there have been many Chinese epidemiological studies of depressive symptoms or disorder in recent years, no clinical or population-based study of a broad list of somatic symptoms in Chinese people could be found in the literature. One reason for this situation could be the lack of a reliable and valid instrument. Using a general population sample, the present study therefore examined the internal consistency, test–retest reliability and construct validity of the Chinese PHQ-15.
Section snippets
Sampling
Over 99% of the domestic households in Hong Kong have a telephone at home, and very few of them have more than one telephone line [16]. Thus, sampling telephone lines based on the updated residential telephone directory should generate a representative sample of households. In each successfully contacted residential unit in the present survey, only one person was interviewed. Among the 11,120 potential contacts, 3014 successfully completed the interviews, 1625 had no suitable interviewees, 4004
Internal consistency and test–retest reliability
The Cronbach's α of the PHQ-15 was 0.792, indicating a moderate and acceptable degree of internal consistency. There were mild to moderate correlations between all the first and retest item scores (rs=0.33–0.66, Ps<.001). They did not differ significantly from one another, except for the item “feeling tired or having no energy” (P=.014). The first (5.85) and retest (5.81) mean PHQ-15 total scores were highly correlated (rs=0.71, P<.001) and did not differ significantly (P=.846). We dichotomized
Discussion
Our results showed that the Chinese PHQ-15 is a reliable instrument for measuring somatic symptoms or somatization in a general population. It exhibited satisfactory internal consistency (Cronbach's α=0.79) in the range reported in previous clinical studies (0.79–0.87) [1], [8], [21]. The PHQ-15 also demonstrated stable 1-month test–retest reliability. The percentage of agreement between the first and retest PHQ-15 outcomes was 91.5%, which was higher than the 80% agreement reported by van
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