This assessment addresses the following learning outcomes: 1. Understand key concepts in statistics and the way in which both descriptive and inferential statistics are used to measure, describe and predict health and illness and the effects of interventions. 5. Apply key terms and concepts of statistics, including; sampling, hypothesis testing, validity and reliability, statistical significance and effectsize. 6. Interpret the results of commonly used statistical tests presented in published literature.
ORIGINAL ARTICLE The rising tide of diabetes mellitus in a Chinese population: a population-based household survey on 121,895 persons Martin C. S. Wong • Michael C. M. Leung • Caroline S. H. Tsang • S. V. Lo • Sian M. Griffiths Received: 27 June 2011 / Revised: 14 April 2012 / Accepted: 16 April 2012 / Published online: 3 May 2012 � Swiss School of Public Health 2012 Abstract Objectives We studied the prevalence of self-reported diabetes mellitus in selected years from 2001 to 2008, and evaluated the factors associated with diabetes. Methods From territory-wide household interviews in a Chinese population in the years 2001, 2002, 2005 and 2008, we evaluated the trend of self-reported diabetes with respect to age, sex and household income. Binary logistic regression analyses were conducted to study the indepen- dent factors associated with diabetes. Results From 121,895 respondents in the household sur- veys, 103,367 were adults aged 15 years or older. Among male respondents, the age- and sex-adjusted prevalence of diabetes in 2001, 2002, 2005 and 2008 was 2.80, 2.87, 3.32 and 4.66 %, respectively; while among female respondents the respective prevalence was 3.25, 3.37, 3.77 and 4.31 %. In all the years, the prevalence escalated with age and increased sharply among the poor. From binary logistic regression analyses, advanced age and low monthly household income were significantly associated with self- report of diabetes. Conclusions This study showed a rising trend of diabetes mellitus in a large Chinese population and found a strong association between population demography and diabetes. Keywords Diabetes mellitus � Prevalence � Age � Gender � Socioeconomic status Introduction Diabetes mellitus imposes a substantial burden to the healthcare system and is recognized as a worldwide health crisis (Feinglos and Bethel 2007). There is an estimated 20.8 million people affected in the US in 2002, and the costs incurred amount to $132 billion (Hogan et al. 2003). The World Health Organization estimates for the number of persons affected by diabetes were 171 millions in 2000 and 266 millions in 2030 (Wild et al. 2004), while the International Diabetes Federation estimates were 246 mil- lions in 2007 and 380 millions in 2025 (International Diabetes Federation 2006). A significant increase in the number of people affected by diabetes is expected in the next few decades. Varying prevalence rates of diabetes were reported in different countries. According to the National Health and Nutrition Examination Survey (NHANES), the prevalence of diabetes was 9.3 % among adults aged 20 years or older (Cowie et al. 2006). In the UK, the prevalence of type 2 diabetes was 3.2 and 4.7 % in Europoid men and women, respectively; while among Asians living in the same city of Coventry, the respective figures were 12.4 and 11.2 % (Simmons et al. 1991). It was found that the higher prev- alence of diabetes in Asians than the Europoids were not attributable to obesity, implying that a lesser extent of excess of adiposity is required in Asians than in Europoids for the development of diabetes. Ethnicity therefore plays an important role in precipitating diabetes. The International Collaborative Study of Cardiovascular Disease in Asia conducted in 2000–2001 found that the M. C. S. Wong (&) � M. C. M. Leung � S. M. Griffiths School of Public Health and Primary Care, Faculty of Medicine, Chinese University of Hong Kong, 4/F, School of Public Health and Primary Care, Prince of Wales Hospital, Shatin, NT, Hong Kong SAR, China e-mail: wong_martin@cuhk.edu.hk C. S. H. Tsang � S. V. Lo Food and Health Bureau, The Government of the Hong Kong Special Administrative Region, Hong Kong SAR, China Int J Public Health (2013) 58:269–276 DOI 10.1007/s00038-012-0364-y 123 prevalence of self-reported diabetes was 1.3 % (Gu et al. 2003), and the age-standardized true prevalence of diabetes was higher in subjects living in northern compared to southern China (7.4 vs. 5.4 %, p \ 0.001). In addition, those living in urban areas had higher prevalence than residents in rural areas (7.8 vs. 5.1 %, p \ 0.001). Hong Kong is one of the most rapidly developing economies in Asia (Leung et al. 2005); its westernization, urbanization and cultural mix due to population mobility could con- tribute to a higher diabetes prevalence. Previous studies in Hong Kong showed that the prevalence ranged from 2 % in people aged \35 years to 20 % in those 65 years or older (Chan et al. 2009; Department of Health, The Government of Hong Kong Special Administrative Region 2012; Janus et al. 2000). The incidence of diabetes is increasing in Hong Kong, but more than half of those affected remain undiagnosed (Janus et al. 2000; Wong and Wang 2006). By 2025, it was estimated that 12.8 % of the Hong Kong population, or 1 million people, will suffer from diabetes (Diabetes Hong Kong 2008). However, there is a scarcity of large-scale studies which adopted a representative sampling methodology in recent years to inform public health policy. The objectives of this study are to evaluate the preva- lence of self-reported diabetes by territory-wide household surveys representative of the whole Hong Kong population, and examined the factors independently associated with diabetes. Methods Sampling frame and methodology The detailed methodology has been described elsewhere (Leung et al. 2005; Census and Statistics Department 2010). The Census and Statistics Department, the Gov- ernment of the Hong Kong Special Administrative Region commissioned Thematic Household Surveys (THS) on health-related issues in 2001, 2002, 2005 and 2008. A major objective of these surveys was to collect information on the health status of the Hong Kong population. The household surveys included all the land-based population of Hong Kong who were residents in non-institutional settings. They excluded hotel transients, persons residing on board vessels and foreign live-in domestic helpers. The survey field works in 2001, 2002, 2005 and 2008 were conducted in the time periods Jan 2001–May 2001; May 2002–July 2002; Nov 2005–Mar 2006 and Feb 2008–May 2008, respectively. Based on a sample of quarters selected from all per- manent quarters and quarters in segments which are for residential and partially residential purposes in Hong Kong, these household surveys were conducted in accordance with a scientifically designed sampling scheme. The pres- ent study adopted a stratified random sampling meth- odology. The sampling units included permanent quarters in built-up regions and segments in non-built-up regions. The Register of Quarters consists of computerized records of all addresses of permanent quarters in built-up regions. These regions included urban areas, new towns and other major developed areas. Unique address was used to iden- tify each unit of quarters with information like street name, building name, floor and flat number. The Register of Segments consists of records of segments in non-built-up areas, identified by relatively permanent and delineated landmarks like footpaths and rivers. The household surveys covered approximately 96 % of the total Hong Kong res- ident population. The approximate response rates for these household surveys were 75 %, consistently across all four survey rounds. Interviewers and survey instrument The design of the surveys obtained input from the Hong Kong Government. A Research firms commissioned by the Census and Statistics Department of Hong Kong trained all interviewers using a standardized method for face-to-face interviews. The survey question related to the outcome variable was ‘‘Do you have any disease that require long- term follow-up by doctors?’’ in 2001; the wordings of the corresponding questions in the other two rounds are slightly different; specifically, ‘‘Have you ever been diag- nosed by a doctor to suffer from the following chronic/ long-term diseases?’’ in 2002; and ‘‘Do you have the fol- lowing chronic or long-term disease(s) diagnosed by a medical doctor, which require long-term follow-up?’’ in 2005. The corresponding question in 2008 was ‘‘Have you ever been told by a western medicine practitioner that you had the following chronic health conditions?’’ If the respondents gave a positive reply, they were further asked whether they had diabetes. The interviewers also recorded demographic information such as age, sex and monthly household income. Outcome variables and statistical analysis STATA version 8.0 was used for all data analysis. The primary outcome variable was rates of self-reported dia- betes mellitus, defined as a positive reply to the above- mentioned questions. We studied the proportion of survey respondents having diabetes in 2001, 2002, 2005 and 2008, and compared the trends according to age, sex and income as a proxy measure of socioeconomic status. We used age- and sex-adjusted prevalence rates taking into account changes in population demography across the years. A 270 M. C. S. Wong et al. 123 binary logistic regression model was conducted with self- reported diabetes as the outcome variable. Age (referent 0–39 years), sex (referent female) and monthly household income (referent C $50,000) were used as covariates in the regression analysis. To explore any heterogeneity in asso- ciation between increasing age- and self-reported diabetes among men versus women, we stratified all subjects according to sex and similar regression analyses were run separately for male and female groups. P values B0.05 were regarded as statistically significant. Results A total of 33,609, 29,561, 29,802 and 28,923 interviews were successfully conducted in the years 2001, 2002, 2005 and 2008, respectively. Among them, 103,367 were adults aged 15 years or above. Their average age was 38.2 years. Table 1 illustrated the distribution of age, sex and monthly household income of the respondents. In general, the respondents were older and had higher monthly household income in surveys conducted in more recent years (both p \ 0.001) (Table 1). The characteristics of respondents were different which implied a change in population structure since the sample methodology was similar across the years. The age-adjusted prevalence of diabetes among male adults was 2.80, 2.87, 3.32 and 4.66 % in years 2001, 2002, 2005 and 2008, respectively. Among female adults, the respective prevalence was 3.25, 3.37, 3.77 and 4.31 % (sex-specific logistic regression models, all p \ 0.001) (Fig. 1; Tables 2, 3). The adjusted prevalence in both sex groups showed a drastic rise with increasing age. There was a progressive rising trend of self-reported diabetes across the years 2001–2008 in the age groups C75 years. From logistic regression analysis using year 2001 as a reference controlling for age, the relative rates of increase Table 1 Respondent characteristics (N = 121,895) in the household face-to-face interviews conducted in Hong Kong, China by stratified random sampling of living quarters in the whole territory in the years 2001, 2002, 2005 and 2008 All 2001 (n = 33,609) 2002 (n = 29,561) 2005 (n = 29,802) 2008 (n = 28,923) No.