Lifetime depressive episodes (‘DSM’) were experienced by 4.8% of men and 8.1% of women; of these participants, 18.9% had had more than one episode. 1.6% were currently experiencing a DSM episode, and 2.7% had experienced such an episode over the past year. Lifetime episodes that met ‘DSM excluding impairment’ criteria were experienced by 8.0% of men and 13.9% of women. A two-week period of feeling depressed or loss of interest (‘D-probe’) was experienced by 13.4% of men and 17.9% of women ().
The prevalence of depression among different socio-demographic groups, according to different definitions of disorder.
3.2. Socio-demographic factors
The socio-demographic characteristics of the participants meeting the three definitions of depression are presented in . Female sex, middle/old age, Sinhala ethnicity, being previously married and having been at school for less than ten years were all associated with depression regardless of the lifetime-ever definition used, and the same trends were seen in those with current or past year DSM depression, although the broader definitions lent more statistical power to test associations. Twin/non-twin status was not associated with depression. There was no main effect of living in an urban rather than a semi-urban area of Colombo, however this covered up an interaction effect with sex (z = 2.65, P = 0.008) for ‘DSM excluding impairment’: urbanicity was associated with depression in men but not in women.
Adjusted odds ratios for the ‘DSM excluding impairment’ definition of depression confirmed that these factors were independently associated with depression, and all were included as potential confounders when examining environmental associations below (although age was entered in years rather than as quartile categories when included as a confounder to avoid over-aggregation). Never married status was associated with lower rates of depression, but this association was not retained once controlling for the other factors, suggesting confounding by age (just 8% of participants in their 40 s had never been married). We further explored the finding of lower depression among the ‘non-Sinhala’ group, and found that it only held among the Moor group (OR = 0.42, P < 0.01).
3.3. Symptom profiles
Among participants who had had a lifetime-ever DSM episode of depression, an average of 7.0 symptoms were endorsed. The percentage who endorsed items one (depressed mood) and two (loss of interest) was very high (94% and 91%) because at least one of these symptoms is required by definition (). Changes in appetite or weight were common, but this was almost entirely accounted for by decreases rather than increases. The most frequently endorsed other items were insomnia, lack of energy and lack of concentration; over half of those affected reported thoughts of death. Psychomotor symptoms were relatively common (present in over half of cases), but the ‘guilt’ item was rare (just 20%). Similar patterns were seen when the affected group was restricted to those who currently or in the past year met a DSM definition.
Endorsement of symptom items among depressed participants, according to different definitions of disorder.
The percentage endorsement of each symptom was lower when the requirement for impairment was removed. However, there was no evidence of a qualitative difference: the reduction in endorsement was at most seven percentage points, rather than certain items marking out those people who were in the full DSM definition group. This was tested using two regression models on the participants who qualified on at least the ‘DSM excluding impairment’ definition. First, impairment status was associated with symptom score (OR = 1.60, 95% CI 1.39–1.85). Second, impairment status was associated with nine variables representing the difference between total symptom score and each of the nine symptoms (i.e. the incremental effect of each symptom). In this second model, the coefficients relating to each symptom could be equated (Wald test of Eq. of parameters: χ2 = 8.10 for 8df, P = 0.42), indicating that although total symptom score was higher in impaired participants, there was no systematic elevation of particular symptoms. Similarly, the ‘D-probe’ group compared to the ‘DSM excluding impairment’ group had fewer endorsements for each item, and this reduction appeared uniform across different symptoms.
The symptom profile for the ‘DSM excluding impairment’ definition was further analysed by sex, which revealed sex-invariance for all but two items (at P < 0.01), and the differences were not large. Depressed men experienced significantly more hypersomnia (29%, versus 17% in women), and depressed women experienced significantly more thoughts about death (57%, versus 44% in men).
3.4. Standard of living
The composite standard of living (SoL) variable was associated with depression (‘DSM excluding impairment’ definition) (). However, there was a significant interaction with sex (z = −2.24, P = 0.049), and when stratified by sex, the association was only seen in males. By splitting the whole sample into quintiles based on SoL score, it was observed that the bottom two quintiles (40th percentile and below) were more likely to be depressed, but there was little evidence of a dose–response relationship (). Again this effect was specific to males (OR = 1.76, 95% CI 1.30 – 2.36 for men in the bottom 40% compared to the top 60%, ).
The relationship between depression (‘DSM excluding impairment’ definition) and standard of living.
Prevalence of depression (‘DSM excluding impairment’ definition) according to sex and standard of living quintile.
In order to investigate why low levels of standard of living appeared to be associated with depression among men only, we divided the sample into four groups according to sex and high/low SoL (40th percentile cut point) (). This revealed that being previously married (i.e. being a widow(er), separated or divorced) was a risk factor for depression among all four sex-by-SoL groups. However, working for some but not all months of the past year was a risk factor only in men of low SoL (adjusted OR: 1.71 (1.07–2.75), employment for 1–10 months compared to 11–12 months). In contrast, only among women of low SoL, those who did not work at all were significantly less depressed (adjusted OR: 0.59 (0.42–0.82) employment for 0 months compared to 11–12 months). No effects were seen in the high SoL groups, so it seems that the association of work pattern with depression is moderated by standard of living.
The influence of marital and occupational status on depression, stratified by standard of living.
Finally, we examined the effect of binary risk components that contributed to the lower end of the SoL composite. We found that, after adjusting for socio-demographic variables, participants' reports of financial wellbeing were associated with depression regardless of sex (). However, poor quality structural materials, poor access to toilet or water facilities, and recent hunger due to poverty were all associated with depression only among men.