Major depression is an important determinant of population health status for 3 reasons. First, the prevalence is very high—4.5% annually, according to the Canadian Community Health Survey, Mental Health and Well-being (see http://www.statcan.ca/english/freepub/82-617-XIE/ index.htm). Second, major depression is associated with impairments in functioning and well-being comparable to impairments associated with other major medical conditions (1). Third, major depression contributes to premature death, with a relative mortality of approximately 1.7 (2). Several countries have adopted public health initiatives against this condition (3,4; see www.health.gov.au/depression/). As reviewed by Katon (3), many initiatives sought to increase treatment utilization and to improve clinical outcomes through professional education and disease management.
In Canada, there has been no national initiative against major depression. Nevertheless, the Canadian public health care system should, in principle, be capable of delivering necessary services in a way that is both accessible and effective. Over time, the stigma associated with mental illness may be diminishing, potentially leading to improved rates of treatment utilization and acceptance. Further, the Canadian Psychiatric Association has supported the development and dissemination of clinical practice guidelines for depressive disorders (4). Two Canadian studies examine utilization rates in localized populations: 1 in Edmonton (5) and 1 in Ontario (6,7). Bristow recently published a review of studies examining treatment seeking for major depression (8). The published literature shows a trend toward higher rates of treatment seeking in more recent years.
Data collected by Statistics Canada in the National Population Health Survey (NPHS) offer a unique opportunity to track the utilization of various health care services over time in a longitudinal cohort in Canada. Data have shown that, between 1994 and 1998, antidepressant (AD) use in Canada increased (9). In this paper, previously reported results from the NPHS are updated to 2000, and the analysis is extended to include additional indicators of health service utilization.
The NPHS is a longitudinal study of a probability sample of the Canadian national population, with the exception of military bases, Native reserves, and some remote areas. The original NPHS survey took place during 1994 through 1995 and included 17 626 subjects. Of these subjects, 14 713 were aged over 15 years and are included in the current analysis. Subsequently, the cohort has been reinterviewed every 2 years, and data from the 1996–1997, 1998–1999, and 2000–2001 survey iterations have been released by Statistics Canada. Response rates have generally been high, and attrition at individual cycles has been relatively low (Table 1). The analyses presented here derive from 9438 eligible subjects aged over 15 years in 1994–1995, with complete data collection at each follow-up interval.
The NPHS interview asks respondents to produce medication containers for all medications taken in the 2 days preceding the interview. Medication names are recorded and coded using Anatomic Therapeutic Classification (ATC) codes (10). The NPHS employed a brief predictive instrument designed to identify probable episodes of major depression in the year preceding the interview. The instrument, called the Composite International Diagnostic Interview Short Form for Major Depression (CIDI-SFMD), was originally developed by Kessler and colleagues (11). Validation studies suggest that the CIDI-SFMD is sensitive but may be somewhat non- specific (12,13) for major depressive episodes (MDEs). The CIDI-SFMD provides a 12-month period prevalence estimate. Period prevalence refers to the proportion of the population meeting DSM-IV criteria for major depression at any time in the preceding year.
The NPHS measured treatment utilization in various ways other than medication use. The interview also included an item evaluating whether subjects had consulted with a health professional about their mental health and an item evaluating the frequency of these consultations. Additional indices of health care utilization not specific to mental health were covered in the NPHS interview: overnight stays in hospital; frequency of consultations with family physicians, social workers, nurses, and alternative health care providers; and participation in self-help groups.
The NPHS sampling procedure included both clustering and unequal selection probabilities. Statistics Canada recommends estimation of variance for statistical procedures using bootstrap methods and publishes an SAS program called BootVar.SAS (14), which was used in this analysis to carry out the variance calculations. Sampling weights calculated by Statistics Canada were used in all parts of the analysis, except for the description of sample attrition (Table 1 data are unweighted). The analyses presented here were performed at the Prairie Regional Data Centre on the University of Calgary campus.
In this cohort, the annual prevalence of major depression was highest in 1994–1995 at 5.6% (95%CI, 5.0 to 6.2) and has remained essentially unchanged in the subsequent data collection cycles: 4.6% in 1996–1997, 4.7% in 1998–1999, and 4.8% in 2000–2001. During the 4 data collection cycles, 11.8% of the subjects had an MDE during 1 or more of the interviews. Of these, 81.1% had an episode detected during 1 of the interviews, 13.6% during 2 of the interviews, and 3.7% during 3 of the interviews; 2.1% had an episode detected in each of the 4 data collection interviews. Since the interviews covered four 1-year periods spaced 2 years apart, the frequencies represent only an approximation of the actual number of episodes experienced by the subjects.
During this interval, use of AD medications increased among respondents with past-year episodes of major depression. In 1994–1995, fewer than 15% of Canadians in this category were taking an AD medication at the time of the survey. Figure 1 shows that the frequency doubled in the following 6 years. Most of the increase occurred for serotonin reuptake inhibitors (SRIs) (that is, a group including fluoxetine, fluvoxamine, paroxetine, and sertraline) and for the “other” category. The “other” category included ADs except for SRIs and tricyclic antidepressants (TCAs). Citalopram was also included in the “other” group because it had not been assigned an ATC code at the time of the 2000–2001 NPHS data collection cycle.Figure 1: Rates of antidepressant treatment among subjects with a major depressive episode in the preceding yeara
AD = Antidepressant; SRI = serotinin reuptake inhibitor; TCA = Tricyclic antidepressant
aError bars are 95%CIs
Earlier reports indicate that, while major depression prevalence is high in persons aged under 35 years and declines with age, AD use in this age group is lowest and increases with age, suggesting that AD medications may be underutilized in this strata (15). Data from the 1994–1995 NPHS support these assertions. Among those with complete data collection during the survey, only 6.8% (95%CI, 3.0 to 10.6) of respondents aged 15 to 34 years with a past-year MDE were taking ADs, compared with 21.0% (95%CI, 13.7 to 28.3) of respondents aged 35 to 54 years. Data for older age strata are not reported because of very large coefficients of variation associated with the estimates. However, by 2000–2001 these differences had largely disappeared, with 30.6% (95%CI, 22.0 to 39.2) in the group aged under 35 years reporting AD use and 31.3% (95%CI, 22.8 to 39.9) in the group aged 35 to 54 years reporting AD use.
In 1994–1995, the frequency of AD use among male respondents with a past-year episode was 6.2% (95%CI, 0.0 to 13.3), compared with 15.7% (95%CI, 11.4 to 20.1) among female respondents. However, by 2000–2001 the frequencies were 26.6% in male patients (95%CI, 16.2 to 37.1) and 32.2% in female patients (95%CI, 25.1 to 39.3).
The increase in AD use was observed across educational groups. Among persons with education levels up to and including secondary school graduation with a probable past-year episode, the rate of AD use in 1994–1995 was 10.6% (95%CI, 5.1 to 16.2), increasing to 32.7% (95%CI, 23.7 to 41.8) in 2000–2001. This increase was paralleled by an increase among those with more than secondary levels of education, from 14.6% (95%CI, 9.7 to 19.4) to 28.4% (95%CI, 21.5 to 35.3) in the same time period.
In rural areas, the proportion of respondents with a recent MDE taking ADs at the time of the survey was 13.2% in 1994–1995 (95%CI, 5.9 to 20.6), increasing to 23.8% (95%CI, 12.2 to 35.5) in 2000–2001. In urban areas, the increase was from 13.0% (95%CI, 8.8 to 17.2) in 1994–1995 to 31.4% (95%CI, 24.7 to 38.1) in 2000–2001.
Some evidence suggests that persons with low social support may be less likely to receive AD treatment (8). The NPHS did not consistently include a measure of social support during the study interval. However, there is evidence showing that never-married subjects may have had a lower rate of treatment in 1994–1995 (7.0%; 95%CI, 2.6 to 11.3), compared with married respondents (17.0%; 95%CI, 9.9 to 24.0) and divorced, widowed, or separated respondents (15.6%; 95%CI, 9.1 to 22.0). However, the unmarried subjects experienced a substantial increase in use: by 2000–2001 the rates in these respective groups were 30.7% (95%CI, 19.9 to 41.5) for never-married respondents, 28.7% (95%CI, 20.8 to 36.6) for married respondents, and 36.6% (95%CI, 20.6 to 52.5) for divorced, widowed, or separated respondents.
Several other potential predictors of AD use could not be easily evaluated using the NPHS data. These include the presence of comorbid conditions, illness severity, and patterns of interaction with the health care system. To access the available data, a logistic regression model predicting any AD use across the 1994–1995 to 2000–2001 interval was fitted to the NPHS data. The model incorporated a restriction of activity indicator (indicating impaired functioning because of a health condition), an indicator variable for mental health consultations, and an indicator for chronic medical conditions (Table 2). More complex models incorporating interaction terms are not reported, since these terms did not achieve statistical significance.
Because consultations with health professionals about mental health strongly predict AD use (Table 2), the increasing rates of use over time might represent increased rates of consultation. However, there was no evidence in the NPHS indicating that the consultation rate was changing over time. Rates of consultation about mental health were predictably higher in patients with past-year MDEs (range 44.8% to 49.7%) than in patients without major depression (range 5.2% to 5.4%).
Polypharmacy in the treatment of major depression is usually reserved for recalcitrant cases. An evaluation of polypharmacy was not planned for this analysis, owing to the expected low rates of polypharmacy in the general population. Indeed, in 1994–1995 the proportion of the population being treated with ADs who were taking more than 1 AD was low, at 3.4% (95%CI, 0.4 to 6.4). However, this proportion increased in recent NPHS iterations, and the trend appeared to be continuing (Figure 2). In 2000–2001, the rate of persons with a past-year MDE taking at least 2 ADs was 8.8% (95%CI, 5.2 to 12.4). Notably, wide CIs depict a sizable degree of imprecision in the estimates.Figure 2: Proportion of subjects found to be taking more than 1 antidepressant medicationa
aError bars are 95%CIs
Most (range 77.7% in 1994 to 81.0% in 2000) NPHS respondents reported consultations with family physicians in the preceding year. It was not possible to determine the purpose or content of these visits. Interestingly, at each survey iteration approximately one-third (32.8% to 37.4%) of subjects with an MDE reported 6 or more consultations with family physicians, compared with only 14.3% to 16.0% of those without major depression. Although these estimates cannot quantify the extent of primary care management of major depression, they do emphasize the considerable extent of contact between persons with MDEs and the primary care system. In all data collection cycles since 1996, over 90% of those with MDEs reported 1 or more visits to a family physician.
The NPHS did not collect data about visits to psychiatrists. However, the proportion reporting visits to nurses, social workers, and psychologists was recorded. The survey data could not confirm that these visits specifically included treatment for major depression. Of those with MDEs, the proportion reporting 6 or more consultations with a nurse nearly doubled, from 3.7% (95%CI, 1.1 to 6.4) in 1994 to 6.2% (95%CI, 3.5 to 8.8) in 2000. In comparison, at each data collection cycle, less than 2% of those without an MDE reported 6 or more visits to a nurse. The proportion reporting 6 or more visits to a social worker also increased in this interval, from 5.6% (95%CI, 3.3 to 8.0) to 10.8% (95%CI, 6.7 to 14.9). In contrast, among those without an MDE, the proportion reporting this number of visits ranged between 1.2% and 2.5%.
The proportion of subjects with an MDE who reported 6 or more visits to a psychologist in 1994 was 6.8% (95%CI, 4.0 to 9.6), which increased slightly in 2000 to 7.9% (95%CI, 4.5 to 11.2). As with the utilization estimates for nurses and social workers, the associated CIs were wide: data were consistent both with larger increases and with no increase in the population. Of the population members without an MDE, less than 1% reported 6 or more consultations with psychologists at all data collection cycles.
Another change documented by the NPHS involved the rate of consultation with alternative practitioners. Reasons for these consultations were not recorded in the NPHS, but it was possible to stratify the consultation rates by probable major depression status. Figure 3 presents the results. There was a general increase in the rates of consultation with alternative practitioners, but the increase was larger in those with probable major depression. In 1994–1995, the rates of consultation with alternative practitioners among persons with a recent MDE was 3.4% (95%CI, 1.8 to 5.0), which was similar to that of respondents without probable depression, at 2.7% (95%CI, 2.2 to 3.2). However, by 2000–2001 the proportions rose to 11.8% (95%CI, 7.7 to 15.9) for those with an MDE and 5.8% (95%CI, 5.2 to 6.4) for those without. In the interval covered by the NPHS, there was an approximate tripling of the rate of consultation with alternative health professionals among subjects with probable MDEs in the preceding year.Figure 3: Rate of consultation with alternative practitioners by major depression statusa
aError bars are 95%CIs
The NPHS recorded the frequency of overnight stays in hospital, but did not document reasons for these admissions. The NPHS data provided no evidence of increasing or decreasing rates of hospitalization for persons with MDEs as an aggregate group. However, when stratified for urban vs rural status, an interesting pattern emerged (Figure 4). The data suggested an increase in rates of overnight stays in hospital for rural residents with major depression. As indicated by the width of CIs in Figure 4, these estimates are subject to a considerable degree of imprecision.Figure 4: Proportions reporting an overnight stay in hospital, by major depression status among rural respondentsa
aError bars are 95%CIs
This analysis identifies shifts in the pharmacoepidemiology of AD use in the Canadian population. In the late 1990s, the frequency of AD use increased. Also, the pattern of use has changed. Many of the groups with previously low frequencies of AD treatment, particularly men and persons aged under 35 years, show a disproportionate increase in the frequency of AD use. The increased use of AD medications was not mirrored by a growth in the proportion of the population reporting consultations with health professionals regarding their mental health. Although such consultations were predictive of AD use, changes in the frequency of consultation did not occur over time and therefore cannot account for increased use of medications. Rather, the data suggest a change in practice patterns, which could be related to changes in the prescribing patterns of physicians or to greater public acceptance of these medications.
Another change in prescribing patterns is evident in the frequency with which more than 1 AD was being taken: in 2000, nearly 9% of respondents taking ADs were taking more than 1 AD. There are several possible explanations for this. First, with growing use of AD medications in the treatment of major depression, clinicians may increasingly be faced with situations of inadequate response or relapse and may possibly be responding to these situations by combining ADs. Alternatively, the trend may reflect increases in the use of certain ADs for symptomatic management (for example, sedating ADs in lieu of sedative hypnotics for the treatment of insomnia) or for the treatment of comorbid psychiatric or medical disorders. However, the reasons for using specific medications were not recorded in the NPHS. Electro- convulsive therapy, another form of treatment for major depression, was not evaluated in the NPHS.
In some respects, annual period prevalence is a problematic way of evaluating treatment utilization, particularly in relation to current medication use, as evaluated in the NPHS. Having a past-year episode is not necessarily an indication of current treatment need. Canadian clinical practice guidelines recommend the continued use of AD medications for 6 months after recovery from an initial uncomplicated episode (16). The proportion of subjects with an episode in the preceding year who are currently taking ADs may, for this reason, under- estimate the proportion of people whose treatment needs have been met (17). Also, some MDEs may resolve spontaneously or respond to nonpharmacologic treatment. Finally, since the CIDI-SFMD may be somewhat nonspecific, some episodes identified may represent adjustment disorders or grief reactions that need not be treated with ADs. For all these reasons, AD treatment rates calculated from the NPHS should not be interpreted as representing a simple proportion of the population whose treatment needs are being met. Neither should the treatment rates calculated from the NPHS be interpreted with reference to a 100% target.
Changes in patterns of health care utilization among persons with major depression are not restricted to the use of AD medications. Rates of contact with some health professionals have increased. The NPHS found an approximate doubling of the frequency with which persons reporting a MDE in the past year also reported seeing a psychologist, nurse, or social worker for 6 or more sessions. This may reflect an increase in the provision of nonpharmacologic treatment. However, the absolute frequency of such visits remained low, and the CIs were wide enough that some observed changes could be caused by chance.
Future research should look beyond the frequency with which people with depression seek or receive treatment and should examine the quality of treatment received, both with respect to medications and with respect to nonpharmacologic treatments. Such research will need to look beyond the medical system, because treatment by other professionals appears to be expanding.
Funding and Support
Dr Patten is a research fellow with the Institute of Health Economics. Dr Beck is a Clinical Fellow in Health Research with the Alberta Heritage Foundation for Medical Research.
This project was supported by a research grant from the Institute of Health Economics.
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Manuscript received May 2003, revised, and accepted February 2004. Previously presented in part at the 52nd Annual General Meeting of the Canadian Psychiatric Association; October 31–November 3, 2002; Banff (AB).
1. Associate Professor, Department of Community Health Sciences and Psychiatry, University of Calgary, Calgary, Alberta.
2. Clinical Assistant Professor, Department of Psychiatry, Foothills Medical Centre, University of Calgary, Calgary Alberta.
Address for correspondence: Dr S Patten, 3330 Hospital Drive NW, Calgary, AB T2N 4N1
Originally published in the May 2004, Volume 49, number 5, print edition with the inadvertent exclusion of Dr Cynthia Beck as coauthor. It has been revised for the electronic edition.
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