Psychiatric illnesses such as depression and anxiety disorders are important health concerns. Owing to substantial morbidity and mortality, they impose a significant burden on the health care system (2,3). Traditionally, they were believed to be predominantly disorders of the middle-aged and elderly (4,5). However, several studies in Canada (6–9) and the US (10) demonstrate significantly higher rates of mental illness—most notably depression and anxiety—in adolescents and young adults than in the middle-aged and elderly. Further, across all age groups, many disorders are more prevalent in women than in men—particularly, mood, anxiety, and eating disorders (4,7,10).
The higher rates of depression and anxiety in younger people have been observed in studies measuring 1-year prevalence rates (7,8,11,12), as well as in studies measuring lifetime rates (4,9,10). This finding has led to the suggestion that, during this century, the prevalence of many mental disorders is increasing, and the onset-age is decreasing, with successive birth cohorts (4,5).
Previous studies in Canada and the US have also described the 12-month use of health services to treat mental illness, with the primary focus on affective disorders, anxiety disorders, and substance abuse disorders (2,13–15). Unmet need for health services in the US was further defined in a study relating lifetime prevalence of these illnesses to lifetime and 12-month use of health care resources (10). Data relating lifetime and 12-month illness prevalence to the use of health care resources have not previously included less common disorders such as obsessive–compulsive disorder (OCD), posttraumatic stress disorder (PTSD), and anorexia (AN) or bulimia (BN); previously reported rates may be underestimating the unmet need.
This paper describes data collected from Ontario women on the lifetime prevalence of depression, anxiety disorders, PTSD, OCD, and AN or BN. We examined the onset-age of these diseases for successive birth cohorts. Moreover, to further define the need for mental health services in the community, we relate the lifetime presence of these disorders to the lifetime use of mental health services.
Survey respondents were drawn from control subjects in the Women’s Health Study (WHS), a case–control study that employed a self-administered mailed questionnaire to examine the association between the use of various medications and breast cancer risk in Ontario women (16). All control subjects were identified using the Ontario Ministry of Finance 1996 population-based assessment rolls, which include both homeowners and tenants and list age, sex, and address. We randomly selected control subjects from these rolls to match the age distribution of the breast cancer cases, so that at least 1 age-matched control subject was selected for each case from 9 separate age strata. Of the 5001 women identified as eligible control subjects, 3062 participated, resulting in an overall response rate of 61%. Sampling weights based on the age distribution of women in Ontario were applied to each stratum.
Analyses were focused on the respondents’ self-report of ever experiencing
1 of 5 psychiatric disorders (anxiety disorders, PTSD, OCD, AN or BN, and
depression) and their use of health services related to treating mental
illness. The survey questions on mental illness were originally designed
to collect information for the WHS on possible confounders of breast cancer
and medication use. For efficiency, therefore, we included only 1 question
to assess the lifetime presence or absence of each of the 5 mental disorders;
we did not ask questions on substance abuse. All questions were worded
as, “Have you ever suffered from (disorder)?” and followed by a description
of the symptoms associated with each disorder to help the respondent (see
Table 1). We developed questions based on the diagnostic categories covered
in the DSM-IV (17), the Structured Clinical Interview for DSM-III-R (SCID)
(18), and the National Institute of Mental Health Diagnostic Interview
Schedule (DIS) (19). However, we did not employ the highly structured research
interviews incorporating the explicit DSM diagnostic criteria, because
the questionnaire was self-administered. We included questions on marital
status and education; household income (low, medium, or high) was derived
from categories of income and household size. For each respondent, we also
collected the “ever” use of mental health services (that is, medication,
counselling, electroconvulsive therapy, or hospitalization), along with
age at first treatment and age of most recent treatment. These questions
were worded, “Have you ever received help from a professional (for example,
physician, counsellor, psychiatrist) for (disorder)?” The questionnaire
was extensively pretested by colleagues and a convenience sample of women,
but it was never formally validated.
Owing to stratified sampling methods and unequal probabilities of selection, we weighted all estimates and employed Taylor linearization methods for calculating 95%CIs and adjusted chi-square statistics (1). Six birth cohorts were defined for comparability with previous studies (4,5): earlier than 1925 (cohort 1), 1925 to 1934 (cohort 2), 1935 to 1944 (cohort 3), 1945 to 1954 (cohort 4), 1955 to 1964 (cohort 5), and 1965 or later (cohort 6). The time at risk for each disorder (the survival time) was either the age at which the subject first experienced the problem or, for those who did not report having the disorder, the subject’s age at the time the questionnaire was completed. We used the Kaplan-Meier product-limit estimate to determine the cumulative lifetime prevalence of each disorder for each birth cohort (20). All analyses were performed using Stata version 6.0 (21).
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