Responses are likely to differ by sociodemographic factors [13] . We therefore stratified the sample by gender and by age (,45 years old vs. .45 years old). Education is also likely to have a significant effect but there are difficulties in education stratification in Hong Kong. The age cut-off of 45 years was adopted to account for the introduction in Hong Kong of 6-year compulsory education in 1971 and 9-year compulsory education in 1978 [45] . This means that people aged 45 or above are much less likely to have a tertiary (college/university) level education and less secondary (high school) education than people aged ,45 years old [45] . Moreover, in traditional families in China, a son (who lived with his parents after marriage) was usually more educationally-favoured over daughters (who moved to their in-laws' home on marriage) to ensure support for the parents in their old age, so males usually obtained more education than females [45] . These distinctions were somewhat evidenced by our data which showed that 98% of the respondents aged ,45 compared to 71% of the respondents aged 45 or above (x 2 = 147.69, p,0.001), and 89% of male compared to 80% of female respondents, obtained at least secondary education (x 2 = 17.05, p,0.001). Since the numbers of tertiary educated respondents and primary (elementary) educated respondents were too small to produce stable models, we limited stratification to gender and age only and acknowledge that this also incorporates indefinable education and income effects.