After analyzing the results of a nationwide telephone survey involving nearly quarter of a million people during 2006 and 2008, the US Centers for Disease Control and Prevention (CDC) concluded that 9 per cent of adult Americans had current depression, with 3.4 per cent meeting criteria for major depression.

Reporting in the 1 October issue of their Morbidity and Mortality Weekly Report, MMWR, the federal agency said by state, the percentage of adult Americans with current depression, that is they met recognized criteria for either major depression or “other depression” during the 2 weeks preceding the survey, ranged from 4.8 per cent in North Dakota to 14.8 per cent in Mississippi.

For their analysis, the CDC used data from their 2006 and 2008 state-based Behavioral Risk Factor Surveillance System (BRFSS) survey.

The BRFSS collects information on health conditions and health risk behaviors among the noninstitutionalized US civilian adult population (aged 18 and over). It does not include households that don’t have landlines and people who are institutionalized or homeless.

For many states, the BRFSS is the only available source of timely, accurate data on health-related behaviors, says the CDC.

This report analyzed data from 235,067 adults in 45 states, the District of Columbia DC, Puerto Rico, and the US Virgin Islands, collected in 2006 and 2008.

The survey data was collected by phone, with interviewers asking respondents questions from a BRFSS adaptation of the Patient Health Questionnaire 8 (PHQ-8), which is based on the manual considered to be the “gold standard” for diagnosing major depressive disorders, the DSM-IV (Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition).

PHQ-8 covers eight of the nine criteria described in DSM-IV: the one that is missed out is the one that asks if the respondent has been having thoughts about suicide or self-harm, since interviewers are not in a position to offer appropriate help over the phone.

Participants were classed as having major depression if for more than half of the days of the two weeks up to the interview they met five of the eight DSM-IV criteria, plus one of two additional criteria (having “little interest or pleasure in doing things” or “feeling down, depressed, or hopeless”).

Participants were classed as having “other depression” if they met two, three or four of the eight criteria, including at least one of the two additional ones.

When the CDC analyzed the survey responses they found that:

  • 9% met criteria for current depression, including 3.4% who met criteria for major depression.
  • Prevalence of major depression varied with age: from 2.8% among 18-24 year olds to 4.6% per cent among 45-64 year olds, and then down to 1.6% among those aged 65 and over.
  • Women (4.0%) were significantly more likely than men (2.7%) to report major depression.
  • People without health cover (5.9%) were also significantly more likely to report major depression than those who did have health insurance (2.9%).
  • People currently married (2.2%) were significantly less likely to report major depression than those who were previously married (6.6%) or never married (4.1%).
  • Retirees (1.6%), people in work (2.0%), homemakers and students (3.0%) were also significantly less likely to report major depression than persons unable to work (22.2%).
  • Non-Hispanic whites (3.1%) were also significantly less likely to report major depression than other races (Non-Hispanic blacks 4.0%, Hispanics 4.0%, others 4.3%), as were people with some college history (2.5%) compared with those having less than a high school diploma (6.7%) and high-school graduates (4.0%).
  • Rates of “other depression” followed similar patterns to major depression, with some notable exceptions: eg this was highest among 18-24 year olds (8.1%).
  • There was a wide range on a state by state basis: estimates for any current depression ranged from 4.8% in North Dakota to 14.8% in Mississippi and was mostly concentrated in the southeast of the US.
  • Within these figures, major depression ranged from a low of 1.5% in North Dakota to 5.3% in Mississippi and West Virginia, while “other depression” ranged from 3.2% in North Dakota, 3.6% in Oregon, and 3.8% Minnesota, to 10.2% in Puerto Rico, 9.5% in Mississippi and 9.0% in West Virginia.

The report’s editors noted that this study is somewhat different to other epidemiological studies of depression in that those tend to focus on lifetime or depression in the last 12 months, whereas this BRFSS one used a model that asked questions relating to symptoms occuring the last two weeks before the interview, hence the definition “current depression”.

Nonetheless, in sociodemographic terms, this survey is generally consistent with those other studies, in that those more likely to meet criteria for depression include women, younger and middle-aged adults, those who have never married, and people with less than a high school education.

But, while older adults, like in the other studies, appear less likely to meet the criteria for depression, this could be because they are underrecognized or underreported, commented the editors.

Perhaps the poorly understood higher rate of depression among women could be explained by gender differences in responses to stressful life events, hormonal and genetic composition, said the editors, but we can’t be sure as the evidence is not strong.

Similarly, there is poor agreement among studies about racial and ethnic differences, some reporting there are none and others showing lower rates among minorities compared with whites. This conflicts with the results of this report where the opposite appears to be the case (and other BRFSS studies show likewise): with higher rates of current depression among non-whites.

The editors emphasize the correspondence between these results and the greater risk factors for mental illness among minority ethnic and racial groups, and suggest that:

“Targeted efforts are needed to address racial/ethnic disparities in recognition and treatment of depression.”

They also suggest, drawing attention to the result that persons without health cover were more likely to have current depression, that while seeking care for depression may be more common, for many, lack of health cover, or limited cover for mental health, “remains a major barrier to care”.

“Current depression among adults — United States, 2006 and 2008”
US Centers for Disease Control and Prevention, MMWR October 1, 2010 / 59(38);1229-1235

Written by: Catharine Paddock, PhD