Number 382 + March 30, 2007

Characteristics of Adults with Serious Psychological

Distress as Measured by the K6 Scale:

United States, 2001–04

by Laura A. Pratt, Ph.D., Office of Analysis and Epidemiology; Achintya N. Dey, M.A., Division of Health Interview

Statistics; Alan J. Cohen, M.A., Office of Analysis and Epidemiology

Abstract

Objective—This report estimates the prevalence of serious psychological

distress (SPD) in the noninstitutionalized adult population of the United States, as

measured by the K6 scale of nonspecific psychological distress, and describes the

characteristics of adults with and without SPD. These findings are compared with

results from previous studies of the characteristics of adults with serious mental

illnesses that cause significant disability, such as severe major depression, bipolar

disorder, and schizophrenia.

Methods—The estimates in this report were derived from the Family Core and

Sample Adult components of the 2001–04 National Health Interview Survey,

conducted by the Centers for Disease Control and Prevention’s National Center for

Health Statistics (NCHS). Estimates were calculated using the SUDAAN statistical

package to account for the complex survey design.

Results—The prevalence of SPD was higher among adults 45–64 years old than

younger adults 18–44 years or older adults 65 years and over. Adults with SPD

were more likely to be female, have less than a high school diploma, and live in

poverty, and less likely to be married than adults without SPD. Moreover, those

with SPD were more likely to be obese and to be current smokers. They have a

higher prevalence of ever being diagnosed with heart disease, diabetes, arthritis, and

stroke than persons without SPD. Adults with SPD were more likely to report

needing help with activities of daily living (ADLs) and instrumental activities of

daily living (IADLs). They also used more medical care services such as doctor

visits and visits to mental health professionals than adults without SPD.

Conclusions—The associations between SPD and sociodemographic

characteristics, health status, and health care utilization are similar to the

relationships found between serious mental illnesses (for example, major depression

or schizophrenia) and these same variables. Persons with SPD demonstrate

disadvantage in both socioeconomic status and health outcomes.

Keywords: mental health c mental illness c National Health Interview Survey c K6

Introduction

Mental health is an important

component of overall health. Mental

illnesses cause suffering, disability, and,

more rarely, death. Among working-age

adults, mental illness is a major and

expensive cause of lowered work

productivity (1,2). Among older adults,

mental illnesses increase the risk of

institutionalization (3). The World

Health Organization Global Burden of

Disease Study lists 4 mental illnesses

among the 10 leading causes of

disability worldwide, specifically,

unipolar major depression, bipolar

disorder, schizophrenia, and obsessivecompulsive disorder (4). The Institute of

Medicine estimates that 90% of persons

who commit suicide suffer from a

diagnosable psychiatric disorder at the

time of their deaths (5).

Accurate information about the

prevalence of mental illness and

characteristics of adults with mental

disorders is important in planning

policies for treatment and prevention,

but measuring mental illness in general

population surveys has many challenges.

It is not possible to determine accurately

whether survey respondents have

particular mental illnesses by asking

U.S. DEPARTMENT OF HEALTH AND HUMAN SERVICES 

Centers for Disease Control and Prevention 

National Center for Health Statistics 
2 Advance Data No. 382 + March 30, 2007

them directly because most people with

mental illness do not have contact with

mental health care providers and may be

unaware of their diagnosis (6).

Diagnostic interviews for lay

interviewers, such as the Diagnostic

Interview Schedule (DIS) (7) and the

Composite International Diagnostic

Interview (CIDI) (8), which are based

on the Diagnostic and Statistical Manual

(DSM) (9) criteria used by clinicians to

make diagnoses, tend to be long and

cumbersome. Surveys that measure all

aspects of health cannot afford to

include these instruments on anything

but a sporadic basis. In an attempt to

make information on mental health

easier to collect in nationally

representative general population

surveys, Kessler and colleagues

developed a scale of nonspecific

psychological distress consisting of only

six questions, the K6 (10).

The K6 was developed to identify

persons with a high likelihood of having

a diagnosable mental illness and

associated functional limitations using as

few questions as possible. It measures

nonspecific psychological distress rather

than specific mental illnesses and is

intended to identify persons with mental

health problems severe enough to cause

moderate to serious impairment in

social, occupational, or school

functioning and to require treatment. Its

development and psychometric

properties are described elsewhere (10).

To date, the K6, or the K10—which

is the K6 plus four additional distress

symptom questions—has been used in

general population surveys in Australia,

Canada, the United States, and as part

of the World Health Organization’s

World Mental Health Surveys, in 30

other countries worldwide (11). Since

1997, the K6 has been part of the

National Health Interview Survey

(NHIS), conducted by NCHS (12). The

K6 has also been included on the

Medical Expenditure Panel Survey

(MEPS) since 2004. The MEPS is

conducted by the Agency for Healthcare

Research and Quality (AHRQ) (13) and

follows a subsample of NHIS

respondents. A modified version of the

K6 has been used in the National

Household Survey on Drug Use and

Health (NSDUH), conducted by the

Substance Abuse and Mental Health

Services Administration (SAMHSA)

(14) since 2001.

Researchers have also begun to use

the K6 in contexts other than large,

nationally representative surveys. For

example, some state-based surveys of

Temporary Assistance for Needy

Families (TANF) recipients have used

the K6 to screen for mental disorders

(15). Another investigator has suggested

its use to screen criminal justice

populations for mental illness (16).

Translations of the K6/K10 associated

with the World Mental Health Survey

Initiative led to its use in non-Englishspeaking countries. As the K6 is used

more widely and in different contexts,

the importance of understanding what it

measures increases.

This report uses the 2001–04 NHIS

to describe the characteristics of adults

with K6-measured SPD and to compare

these findings with results of previous

studies of the characteristics of persons

with serious mental illnesses that cause

impairment in role functioning, such as

severe major depression, bipolar

disorder, and schizophrenia, in the

noninstitutionalized population.

Methods

Data source

The NHIS is a continuous face-toface household interview survey that

covers a wide variety of health-related

topics. It is a complex, stratified sample

survey designed to provide estimates for

the civilian noninstitutionalized

population of the United States. Every

year data are collected about all family

members in approximately 40,000

households. More detailed health

information is obtained from one

randomly sampled adult (the ‘‘sample

adult’’) and one randomly sampled child

in each family in the sample. The

present study uses data from the

combined 2001 through 2004 sample

adult interviews for a total of 123,610

persons 18 years of age and older living

in the community. Three variables from

the family questionnaire are also

analyzed. The final response rate for the

2001–04 combined household files was

88.6% and for sample adult files was

73.7%. Data from the sample adult

questionnaire are self-reported, except

when respondents are physically

incapable of responding for themselves.

This study includes proxy-reported data

for 931 sample persons, self-reported

data for 122,591 sample persons, and 88

sample persons without data on

respondent status.

Measurement of SPD

The K6 asks about the frequency of

each of six symptoms of mental illness

or nonspecific psychological distress:

During the PAST 30 DAYS, how

often did you feel...

1.So sad that nothing could cheer you

up;

2.Nervous;

3.Restless or fidgety;

4.Hopeless;

5.That everything was an effort; and

6.Worthless.

The following options are given for

describing frequency:

1.ALL of the time;

2.MOST of the time;

3.SOME of the time;

4.A LITTLE of the time; and

5.NONE of the time.

‘‘None of the time’’ is given a score

of 0, ‘‘all of the time’’ a score of 4 and

the total possible score ranges from 0 to

24. As suggested by Kessler and

colleagues (17), a score of 13 or above

is used to indicate serious psychological

distress. The prevalence rates presented

here are described as 30-day prevalence

rates because the reference period for

the symptom questions is the ‘‘past 30

days.’’

The first validity study using the K6

was done by Kessler and colleagues

(18) with the modified NSDUH version.

That version of the K6 asks about the

same symptoms and uses the same

scoring but has a modified stem

question that asks respondents how

frequently they experienced symptoms

of psychological distress ‘‘during the 1

month in the past year when they were

at their worst emotionally.’’ That version

was tested along with two other

instruments, a greatly abbreviated set of

the Composite International Diagnostic
Advance Data No. 382 + March 30, 2007 3

Interview (CIDI) questions (19) and the

World Health Organization Disability

Assessment Scale (WHO-DAS) (20),

and determined to have the best

sensitivity and specificity of the three

for DSM disorders as measured by the

Structured Clinical Interview for

DSM-IV (SCID) administered by mental

health professionals (18). Validity

studies using the original ‘‘past 30

days’’ stem question are in progress

(21).

Measurement of other variables

Other variables available from the

NHIS and used in these analyses include

sociodemographic characteristics such as

sex, age, race and ethnicity, marital

status, family income, and education.

Family size and family income are used

to define three economic categories:

poor, living below the federal poverty

line; near poor, 100 to less than 200%

of the federal poverty line; and not poor,

living at or above 200% of the federal

poverty line.

Indicators of access to health care

include health insurance status at the

time of interview for persons under 65

years of age and unmet need for health

care due to cost in the past 12 months.

Measurements of health care utilization

include how long it has been since a

respondent saw a doctor, how many

doctor visits a respondent has had in the

last 12 months, and whether the person

has spoken to a mental health

professional in the last year.

Risk factors and health status

measures include smoking, body mass

index (BMI), and the presence or

absence of seven chronic physical

illnesses, all self-reported in the sample

adult interview. Smoking status is

categorized as current, former, and never

smoker. BMI was calculated using

self-reported height and weight and

categorized as underweight (BMI less

than 18.5), normal weight (BMI greater

than or equal to 18.5 but less than 25),

overweight (BMI greater than or equal

to 25 but less than 30), and obese (BMI

greater than or equal to 30). The sample

adult is asked about the following

chronic diseases: chronic lung disease,

heart disease, diabetes, hypertension,

arthritis, cancer, and stroke. The

questions ask if a doctor has ever told

the respondent that he or she had the

disease.

Functional limitations are measured

by any report of needing help in one of

four ADLs—eating, bathing, dressing, or

getting around inside the house, and

four IADLs—everyday household

chores, doing necessary business,

shopping, or getting around for other

purposes. Physical limitations are

measured by difficulty walking onefourth of a mile and difficulty climbing

a flight of steps.

Difficulties in social functioning are

evaluated by three questions in the

NHIS. They include difficulty in

participating in outside activities like

shopping or attending movies or

sporting events; participating in social

activities such as visiting friends,

attending clubs and meetings, or going

to parties; and doing things to relax at

home or for leisure (reading, watching

TV, sewing, listening to music . . .).

Statistical analysis

First, the prevalence of SPD among

persons with selected characteristics is

described. Crude prevalence rates are

shown for each characteristic.

Next, characteristics of persons with

and without SPD are compared and

associations described. To remove the

effect of any differences in the age

distributions of the two groups, the rates

are age adjusted to the year 2000

standard projected U.S. population using

five age groups: 18–44 years, 45–54

years, 55–64 years, 65–74 years, and 75

years and over. Percent distributions and

standard errors are presented. The

statistical significance of differences

between estimates was evaluated using

two-sided t-tests. These tests did not

formally take multiple comparisons into

account, but because of the large

number of tests carried out, the 0.01

level rather than the 0.05 level was used

for significance testing. Differences

discussed in the text were statistically

significant at the p<0.01 level. When a

difference is not described in the text, it

does not necessarily mean that a t-test

was performed and the difference was

found to be not significant.

Because of the large number of

respondents missing family income

information, approximately one-third of

respondents, the analyses that include

poverty status and income use multiply

imputed family income (22). The results

of these analyses are similar to the

results that use only the two-thirds with

reported family income. SUDAAN is

used for all analyses to account for the

complex, clustered sample design of the

NHIS (23).

Results

Prevalence of SPD

The crude 30-day prevalence rate of

SPD in the noninstitutionalized adult

population of the United States was

3.1% over the 4 years from 2001–04

(Table 1). The prevalence was highest in

middle-aged adults 35–64 years old,

lower in younger adults, and lowest in

adults 65 years of age and over. The

1-month prevalence rate of SPD was

higher in women (3.9%) than men

(2.4%) overall and in every age group,

although the difference did not reach

statistical significance in persons 65–74

years of age (Figure 1). Persons living

below the poverty line had a prevalence

rate of 8%, four times as high as that of

persons with family income at 200% of

the poverty line or higher (2%).

Hispanic adults aged 65 years and

over had a higher prevalence of SPD

(5.9%) than did non-Hispanic white

adults (2.1%) or non-Hispanic black

adults (2.4%) in the same age group

(Figure 2). In contrast, there was no

significant difference in prevalence rates

of SPD by race and ethnicity among

adults 18–44 years old. Among Hispanic

adults, the prevalence of SPD was lower

(2.7%) in persons aged 18–44 years

(Figure 2) than in persons aged 45–64

years (5%) or persons 65 years of age

and over, while among non-Hispanic

white adults, the prevalence of SPD in

persons 65 years of age and over (2.1%)

was the lowest of any age group.

In each race and ethnicity group,

the prevalence of SPD was much higher

among poor respondents (those living

below the federal poverty threshold)

than among those at higher incomes

(Figure 3). The prevalence of SPD
4 Advance Data No. 382 + March 30, 2007

Men Women 

0 

2 

4 

6 Prevalence and 99% confidence intervals 

Percent

 18–24 25–34 35–44 45–54 55–64 65–74 75 and 

over 

DATA SOURCE: National Health Interview Survey, 2001–04. Data are based on household interviews of a 

sample of the civilian noninstitutionalized population. 

Age 

Figure 1. Crude 30-day prevalence of serious psychological distress by age and sex,

National Health Interview Survey 2001–04

Non-Hispanic 

black 

Non-Hispanic 

white 

Hispanic 

Prevalence and 99% confidence intervals 

Percent 

0 

2 

4 

6 

8 

10 

18–44 45–64 65 and over 

Age group 

DATA SOURCE: National Health Interview Survey, 2001–04. Data are based on household interviews of a sample 

of the civilian noninstitutionalized population. 

(34%) than adults without SPD (17%),

and much less likely to have received a

college degree (9%) than adults without

SPD (25%). Forty-four percent of

persons with SPD had a family income

of less than $20,000 per year, while

only 20% of persons without SPD had

this level of income. Persons with SPD

were less likely to live with other family

members (76%) than were persons

without SPD (81%). They were also

twice as likely to be divorced (24%

versus 12%). Persons with SPD were

slightly more likely to live in rural areas

(nonmetropolitan statistical areas) than

persons without SPD.

Health status and health behaviors

In age-adjusted comparisons, almost

one-half of persons with SPD had fair

or poor health, while only 11% of

persons without SPD had fair or poor

health (Table 3). Persons with SPD were

at least twice as likely to have ever been

diagnosed with heart (14%) or lung

disease (24%), diabetes (13%), arthritis

(40%), or stroke (8%) than were persons

without SPD. They were also twice as

likely to have two or more of the seven

selected chronic diseases (35%

compared with 17%).

Forty-two percent of persons with

SPD were current cigarette smokers as

compared with 21% of persons without

SPD. They were also more likely to be

obese (33% compared with 23%).

Access to and utilization of health

care services

Persons with SPD were much more

likely to forgo needed health care

Figure 2. Crude 30-day prevalence of serious psychological distress by race or ethnicity

and age, National Health Interview Survey 2001–04

among poor non-Hispanic white adults

(9.2%) was higher than among poor

Hispanic adults (6.4%). Among not poor

respondents (those living at 200% of the

poverty threshold or higher), there was

no significant difference in the

prevalence of SPD among non-Hispanic

blacks (1.6%), non-Hispanic whites

(1.9%), or Hispanics (2.1%).

Characteristics of persons with

and without SPD

Sociodemographic

Table 2 compares the

sociodemographic characteristics of

persons with SPD and persons without

SPD, after adjusting for age differences.

Adults with SPD were more likely to

have less than a high school education

because of cost (Table 4). For example,

18% of persons with SPD needed

mental health care but were not able to

afford it, while only 2% of persons

without SPD had this problem. This

difference may be due to both greater

need for care as well as less access to

care among those with SPD. Persons

with SPD were more likely to need

dental care and be unable to afford it

(32%), and they were more likely to be

unable to get needed prescription drugs

because of cost (32%) than were

persons without SPD (10% and 7%

respectively). Persons with SPD were

more than four times as likely to have
Advance Data No. 382 + March 30, 2007 5

Prevalence and 99% confidence intervals 

Percent DATA SOURCE: National Health Interview Survey, 2001–04. Data are based on household interviews of a sample 

of the civilian noninstitutionalized population. 

0 

2 

4 

6 

8 

10 

Poor Near-poor Non-poor 

Poverty status 

Non-Hispanic 

black 

Non-Hispanic 

white 

Hispanic 

Figure 3. Age-adjusted 30-day prevalence of serious psychological distress by race or

ethnicity and poverty, National Health Interview Survey, 2001–04

Serious No serious Prevalence and 99% confidence intervals 

Percent DATA SOURCE: National Health Interview Survey, 2001–04. Data are based on household interviews of a sample 

of the civilian noninstitutionalized population. 

0 

10 

20 

30 

40 

psychological distress

 18–44 45–64 65 and over 

Age group 

Among adults younger than 65 who had

SPD, 36% spoke to a mental health

professional within the past 12 months

(Figure 4).

Functional limitations

Persons with SPD were more likely

to have functional limitations than

persons without SPD (Table 5). Persons

with SPD were more than six times as

likely to need help with ADLs (9%) and

IADLs (19%) than were persons without

SPD (1% and 3%). They were also

more likely to have vision (27%) and

hearing impairment (8%) than persons

without SPD (9% and 3%). A larger

proportion of persons with SPD had

difficulty walking (41%) and difficulty

climbing a flight of stairs (35%) than

did persons without SPD (10% and 7%).

Thirty-four percent of persons with SPD

had difficulty getting out to go

shopping, to the movies, or other events,

and 32% of persons with SPD had

difficulty in social activities compared

with less than 5% of persons without

SPD. Eighteen percent of persons with

SPD had difficulty with relaxing at

home by reading, watching TV, or

listening to music compared with less

than 2% of persons without SPD.

Comparisons of the

characteristics of persons with

SPD and persons with serious

mental illness

The Surgeon General’s Report on

Mental Health defines serious mental

illness as mental illness that causes

significant disability. Included in the

category of serious mental illness in the

Surgeon General’s Report are

schizophrenia, bipolar disorder,

Figure 4. Percent reporting any contact with mental health professional by serious

psychological distress and age, National Health Interview Survey, 2001–04

Medicaid as were persons without SPD,

25% and 6%, respectively. They were

also significantly more likely to be

uninsured (29% compared with 19%)

than those without SPD.

Persons with SPD are heavy

utilizers of medical care, consistent with

their poorer health status. They were

more likely to have seen a health care

professional within the last 6 months

(81%) than persons without SPD (69%)

and were three times as likely to have

had 10 or more visits within the past

year (39% compared with 13%).

Thirty-two percent of persons with SPD

talked to a mental health professional

within the year prior to the interview,

substantially more than the 5% of those

without SPD. Among adults with SPD,

those over the age of 65 were least

likely to have seen a mental health

professional: 18% had such contact.

obsessive-compulsive disorder (OCD),

panic disorder, and severe forms of

major depression (3). The report

estimates that 5.4% of American adults

have a serious mental illness in any one

year and that about one-half of the 5.4%

have a serious and persistent mental

illness, generally lifelong conditions.

The 1-month prevalence rate for SPD in

the 2001–04 NHIS of 3.1% is not

inconsistent with these estimates.

As measured by the K6 scale in the

2001–04 NHIS, women have a higher

prevalence of SPD than men in every
6 Advance Data No. 382 + March 30, 2007

age group. Most studies agree that the

prevalence of schizophrenia and bipolar

disorder is the same in men and women

(24,25), while major depression is two

to three times as common in women as

in men (26). OCD is equally common in

women and men, but other anxiety

disorders such as panic disorder and

generalized anxiety disorder are more

common in women (3).

In the 2001–04 NHIS, Hispanic

adults 65 years and over had higher

rates of SPD than non-Hispanics of the

same age. The prevalence rate of SPD

in Hispanics 18–44 years of age was

similar to that in non-Hispanic white

and non-Hispanic black persons

(Figure 2). In the 1996 Health and

Retirement Survey (HRS), Hispanic

persons aged 54–65 years had higher

rates of major depression as measured

by the CIDI-SF than did non-Hispanic

white persons (27). Other studies of the

relationship between Hispanic ethnicity

and prevalence of various mental

illnesses have found lower rates among

Hispanics than other ethnic groups

(28–32), but age-stratified results were

not presented.

Persons with SPD demonstrated

social disadvantage in the 2001–04

NHIS. Persons with SPD were more

likely to be poor (live below the federal

poverty line) than persons without SPD.

Persons with SPD were much less likely

to be married or have finished their high

school education than persons without

SPD. The higher rate of poverty among

seriously mentally ill persons is a

common finding (33–34). In a series of

three papers describing the social

consequences of psychiatric illness,

Kessler and colleagues (35–37)

demonstrated that early-onset psychiatric

illness is associated with lower

educational achievement, higher risk of

teenage pregnancy, and inability to find

or maintain a relationship leading to

marriage.

Persons with SPD in the 2001–04

NHIS were more likely to have poor

health and to smoke. Many studies have

reported a relationship between mental

illness, especially major depression and

schizophrenia, and many chronic

diseases, particularly cardiovascular

disease (38–42). The finding that

persons with mental illnesses are more

likely to smoke has been reported many

times with many different mental

illnesses (43–44).

Persons with SPD had more recent

and more frequent interaction with

health care professionals than persons

without SPD. Persons with mental

illness have consistently been found to

be high utilizers of medical care. There

is a large amount of literature

documenting this association, especially

among persons with depression (45–48).

In the 2001–04 NHIS, only 32% of

persons with SPD had contact with a

mental health professional in the

previous year. A single report of contact

with a mental health professional

provides no information on whether a

patient was treated, treated

appropriately, and able to comply with

treatment. Low levels of treatment have

also been reported in other studies. In

the Epidemiologic Catchment Area

Program (ECA) surveys, which took

place between 1981 and 1984,

researchers found that only one-third of

persons with mental disorders received

treatment (49). In the National

Comorbidity Survey (NCS) of the early

1990s, reported treatment rates were

also approximately 33% (50). In the

NCS Replication, fielded from 2001 to

2003, researchers found a slightly higher

percent receiving treatment, 41%, but

found that only one-third of persons

with a disorder who received treatment

received ‘‘minimally adequate

treatment’’ (51).

Persons with SPD in the 2001–04

NHIS had high levels of functional

impairment. High levels of functional

limitations among persons with mental

illness are a consistent finding (52–55).

Symptoms of serious mental illnesses

can directly cause social disability. For

example, inability to concentrate is a

symptom of major depression, and in

severe cases, the concentration required

to read a book or even to follow a

television show is impossible. Persons

with untreated OCD may find

themselves unable to leave home

because of their checking behavior, such

as continuously checking to be sure the

stove is off or continuously checking the

door to be sure it is locked. The

symptoms of all the serious mental

illnesses, including schizophrenia,

bipolar disorder, severe forms of major

depression, and OCD, are not conducive

to forming and maintaining social

relationships. The cross-sectional

relationship of mental illness with

physical limitations in functioning has

also been reported in other studies (56,

57).

Discussion

The characteristics of persons with

SPD as measured by the K6 are the

same as the characteristics of persons

with serious mental illnesses as

described in psychiatric epidemiologic

studies. The associations of SPD with

age, marital status, education, and

income are all in the expected direction.

In accord with what we know about the

epidemiology of serious mental illness

in the general population, K6-measured

SPD is associated with high levels of

functional limitations and high

utilization of medical care. As seen in

other studies of mental illness, only onethird of persons with SPD have seen a

mental health professional in the past

year, an area that deserves further

investigation. This study found higher

rates of SPD in older Hispanic persons

than in other older adults. Replication of

this finding in studies using diagnosisbased measures of mental illness would

be valuable in planning targeted

interventions.

Because of the cross-sectional

design of the NHIS, the direction of

causation of the associations described

in this report cannot be inferred from

these data. Prospective studies that

measure the K6 in respondents at

baseline and then follow the respondents

over time are needed to clarify the

temporal relationships. The Medical

Expenditure Panel Survey (MEPS)

follows a subsample of NHIS

participants for another 2 years,

providing 3 years of data on persons in

the subsample. The MEPS provides the

opportunity to explore some

relationships, particularly between

serious psychological distress and health

care utilization, but the follow-up period

is too short to clarify the temporal

associations between SPD and chronic

illnesses or functional limitations.
Advance Data No. 382 + March 30, 2007 7

A major limitation of the K6 is that

it does not provide information on

which particular psychiatric diagnosis or

diagnoses a respondent may have. Since

1980, psychiatric epidemiology has

concentrated on diagnostic interviews

for general population surveys, so using

the information provided by the K6

requires a paradigm switch. Although

our study documents that SPD measured

by the K6 is related to other covariates

in a similar manner to serious mental

illnesses, it remains difficult to identify

what is being measured. The particular

symptoms included in the K6 as well as

the gender disparity observed makes it

likely that severe, disabling mood and

anxiety disorders are being identified. It

is less clear whether persons with

schizophrenia, the most serious mental

illness, are identified.

In the lay-person interviews used in

psychiatric epidemiologic surveys, such

as the DIS and the CIDI, respondents

answer questions about their own

symptomatology. For reasons probably

related to the diseases themselves,

respondents with psychosis and mania

may not accurately assess or report

whether they have the symptoms

(58–60). It is unclear whether the K6 is

any more successful at capturing

persons with these disorders. Since the

K6 asks about symptoms of distress

rather than particular symptoms of the

illnesses, such as psychosis, it is

possible that the K6 may identify

persons with schizophrenia or bipolar

disorder as having SPD. In addition, we

do not know how many persons

identified by the K6 have disabling

mental health problems that might not

fit into any of the diagnostic categories

described in the DSM. As results from

validation studies related to the World

Mental Health Surveys Initiative become

available, the diagnostic characteristics

of persons with SPD will be clarified.

One limitation of this study is that

many people with the most serious

mental illnesses are either homeless or

institutionalized, and because the NHIS

is a household survey, these people are

not surveyed. Another limitation, shared

by all symptom count measures, is that

persons with serious mental illness who

are being treated successfully will not

be captured by the K6.

A major strength of the K6 lies in

its brevity. It is short enough that it is

feasible to add to lengthy, general health

interviews like the NHIS. As more

researchers use the K6 scale in studies

using the data from the MEPS and the

NSDUH, as well as the NHIS, more

will be learned about its properties and

usefulness.

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10 Advance Data No. 382 + March 30, 2007

Table 1. Crude 30-day prevalence rates (with standard errors) of adults with serious psychological distress, by selected

sociodemographic characteristics: United States, 2001–04

Serious psychological distress1

Standard

Characteristic Percent error

All adults2 ........................................................ 3.1 0.07

Age

18–24 years ....................................................... 2.8 0.18

25–34 years ....................................................... 2.6 0.11

35–44 years ....................................................... 3.3 0.13

45–54 years ....................................................... 4.0 0.15

55–64 years ....................................................... 3.6 0.17

65–74 years ....................................................... 2.3 0.16

75 years and over ................................................... 2.5 0.18

Sex

Male ........................................................... 2.4 0.08

Female .......................................................... 3.9 0.09

Race and ethnicity

Hispanic or Latino ................................................... 3.5 0.15

Not Hispanic or Latino:

White.......................................................... 3.0 0.08

Black or African American ............................................. 3.5 0.19

Other.......................................................... 3.3 0.29

Education

No high school diploma ................................................ 6.2 0.20

High school diploma or GED3 ............................................ 3.3 0.12

Some college, no bachelor’s degree ........................................ 2.8 0.10

Bachelor’s degree or higher ............................................. 1.2 0.07

Poverty status4

Poor............................................................ 8.0 0.32

Near poor ........................................................ 4.8 0.18

Not poor ......................................................... 1.9 0.06

Marital status

Married .......................................................... 2.3 0.07

Never married...................................................... 3.3 0.13

Divorced or separated................................................. 6.2 0.21

Widowed ......................................................... 4.1 0.21

1

Six psychological distress questions are included in the Sample Adult Core component. These questions ask how often a respondent experienced certain symptoms of psychological distress

during the past 30 days. The response code (0–4) of the six items for each person are summed to yield a scale with a 0–24 range. A value of 13 or more for this scale is used here to define

serious psychological distress. 2

Persons of other races and unknown race and ethnicity, unknown education, unknown family income, unknown poverty level, unknown employment status, and unknown marital status are

included in the total but not shown separately. 3

GED is General Educational Development high school equivalency diploma. 4

Poverty status is based on family income and family size using the Census Bureau’s poverty thresholds for the previous calendar year. ‘‘Poor’’ persons are defined as below the poverty threshold.

‘‘Near poor’’ persons have incomes of 100% to less than 200% of the poverty threshold. ‘‘Not poor’’ persons have incomes that are 200% of the poverty threshold or greater.
Advance Data No. 382 + March 30, 2007 11

Table 2. Age-adjusted percent distributions (with standard errors) of selected sociodemographic characteristics among adults, by

presence or absence of serious psychological distress: United States, 2001–04

Psychological distress1

Serious psychological No serious psychological

distress distress

Standard Standard pCharacteristic Percent error Percent error value

All persons2 ...................................... 100.0 . . . 100.0 . . . . . .

Age3

18–44 years ...................................... 48.7 0.91 52.5 0.27 f

45–64 years ...................................... 39.2 0.88 31.5 0.20 f

65 years and over .................................. 12.1 0.58 16.0 0.18 f

Sex

Male........................................... 35.8 0.93 48.2 0.18 f

Female ......................................... 64.2 0.93 51.8 0.18 f

Race and ethnicity

Hispanic or Latino .................................. 13.7 0.62 12.0 0.20 –

Not Hispanic or Latino:

White ......................................... 69.1 0.92 72.1 0.33 f

Black ......................................... 12.2 0.68 10.9 0.25 –

Other ......................................... 5.0 0.46 4.9 0.13 –

Education

No high school diploma ............................... 34.2 0.92 16.5 0.21 f

High school diploma or GED4 ........................... 31.3 0.87 29.4 0.22 –

Some college, no bachelors degree ....................... 25.1 0.76 29.2 0.20 f

Bachelor’s degree or higher ............................ 9.4 0.53 24.8 0.27 f

Family income

Less than $20,000 ................. ................. 44.1 1.05 19.5 0.24 f

$20,000 or more ................................... 55.9 1.05 80.5 0.24 f

$20,000–$34,999 ................................. 23.8 0.85 19.5 0.18 f

$35,000–$54,999 ................................. 15.4 0.73 20.2 0.17 f

$55,000–$74,999 ................................. 7.3 0.56 14.2 0.17 f

$75,000 or more .................................. 9.4 0.80 26.6 0.28 f

Poverty status5

Poor ........................................... 29.2 0.96 11.2 0.19 f

Near poor ....................................... 28.4 0.87 17.8 0.17 f

Not poor ........................................ 42.4 1.00 71.0 0.27 f

Family size

1 ............................................. 23.8 0.70 18.6 0.23 f

2 ............................................. 30.8 0.81 33.1 0.17 f

3 ............................................. 18.6 0.73 18.1 0.15 –

4 ............................................. 13.5 0.70 17.0 0.15 f

5 or more........................................ 13.3 0.71 13.2 0.16 –

Marital status

Married ......................................... 41.9 0.96 58.4 0.25 f

Never married ..................................... 24.8 0.75 22.9 0.22 –

Divorced or separated ................................ 23.5 0.74 12.0 0.11 f

Widowed ........................................ 9.8 0.44 6.8 0.07 f

Place of residence6

MSA, central city ................................... 29.4 1.05 27.9 0.56 –

MSA, not in central city ............................... 46.4 1.25 51.9 0.64 f

Not in MSA ...................................... 24.2 1.10 20.2 0.47 f

. . . Category not applicable.

f p<0.01 for a test of the difference between persons with serious psychologocal distress and no serious psychological distress.

– p≥0.01 for this test. 1

Six psychological distress questions are included in the Sample Adult Core component. These questions ask how often a respondent experienced certain symptoms of psychological distress

during the past 30 days. The response codes (0–4) of the six items for each person are summed to yield a scale with a 0–24 range. A value of 13 or more for this scale is used here to define

serious psychological distress. 2

Persons of other races and unknown race and ethnicity, unknown education, unknown family income, unknown poverty level, unknown employment status, and unknown marital status are

included in the total but not shown separately. 3

Estimates for age groups are not age adjusted. 4

GED is General Educational Development high school equivalency diploma. 5

Poverty status is based on family income and family size using the Census Bureau’s poverty thresholds for the previous calendar year. ‘‘Poor’’ persons are defined as below the poverty threshold.

‘‘Near poor’’ persons have incomes of 100% to less than 200% of the poverty threshold. ‘‘Not poor’’ persons have incomes that are 200% of the poverty threshold or greater. 6

MSA is a metropolitan statistical area.

NOTE: Estimates are age adjusted to the 2000 U.S. standard population using five age groups: 18–44 years, 45–54 years, 55–64 years, 65–74 years, and 75 years and over.
12 Advance Data No. 382 + March 30, 2007

Table 3. Age-adjusted percents (with standard errors) of adults with selected health characteristics, by presence or absence of serious

psychological distress: United States, 2001–04

Psychological distress1

Serious psychological No serious psychological

distress distress

Standard Standard pCharacteristic Percent error Percent error value

Self-assessed health2

Fair or poor ...................................... 49.7 0.89 10.7 0.13 f

Selected risk factors

BMI3

Underweight (less than 18.5)............................ 3.6 0.37 2.0 0.05 f

Normal weight (18.5 to less than 25.0)...................... 34.4 0.91 39.4 0.19 f

Overweight (25.0 to less than 30.0)........................ 28.7 0.83 35.5 0.17 f

Obese (greater than or equal to 30.0) ...................... 33.3 0.89 23.1 0.17 f

Smoker4

Never smokers .................................... 37.3 0.91 56.8 0.21 f

Former smokers ................................... 20.3 0.74 22.1 0.15 –

Current smokers ................................... 42.4 0.88 21.1 0.17 f

Ever diagnosed with selected chronic diseases

Diabetes5........................................ 13.0 0.58 6.4 0.08 f

Hypertension6 ..................................... 39.2 0.87 24.2 0.14 f

Heart disease7 .................................... 14.2 0.6 7.1 0.09 f

Chronic lung disease8 ................................ 24.4 0.84 10.8 0.11 f

Arthritis9 ........................................ 40.4 0.96 20.7 0.16 f

Stroke10 ........................................ 7.7 0.49 2.3 0.05 f

Cancer11 ........................................ 10.3 0.61 6.8 0.08 f

Number of chronic diseases12

None .......................................... 38.8 0.83 60.6 0.17 f

1 ............................................. 26.5 0.80 23.0 0.15 f

2 or more........................................ 34.8 0.85 16.5 0.12 f

f p<0.01 for a test of the difference between persons with serious psychological distress and no serious psychological distress.

– p≥0.01 for this test. 1

Six psychological distress questions are included in the Sample Adult Core component. These questions ask how often a respondent experienced certain symptoms of psychological distress

during the past 30 days. The response codes (0–4) of the six items for each person are summed to yield a scale with a 0–24 range. A value of 13 or more for this scale is used here to define

serious psychological distress. 2

Self-assessed health is based on a question in the survey that asked respondents, ‘‘Would you say [subject’s name] health in general was excellent, very good, good, fair, or poor?’’ This

information was obtained during a part of the interview that allowed proxy responses, such that a knowledgeable adult family member could respond on behalf of adults not taking part in the

interview (however, the data above are based on the reported health status for the sample adult only). ‘‘Fair’’ and ‘‘poor’’ are combined. 3

BMI is body mass index based on self-reported height and weight. 4

Smoking status: Never smoker—have never smoked at least 100 cigarettes in their lifetime. Former smoker—have smoked at least 100 cigarettes in their lifetime, but currently do not smoke.

Current smoker—have smoked at least 100 cigarettes in their lifetime and still currently smoke. 5

Respondents were asked if they had ever been told by a doctor or health professional that they have diabetes or sugar diabetes (if female, other than during pregnancy). 6

Respondents were asked if they had ever been told by a doctor or health professional that they had hypertension. 7

Heart disease includes coronary heart disease, heart attack, and angina. Respondents were asked if they had ever been told by a doctor or health professional that they had any of these

conditions.

8

Chronic lung disease includes chronic bronchitis and asthma. Respondents were asked if they had ever been told by a doctor or health professional that they had either of these conditions. 9

Respondents were asked if they had ever been told by a doctor or health professional that they had arthritis. 10Respondents were asked if they had ever been told by a doctor or health professional that they had a stroke. 11Respondents were asked if they had ever been told by a doctor or health professional that they had cancer or a malignancy of any kind. 12The number of chronic diseases is calculated by counting how many of the seven diseases listed above the respondent reported.

NOTE: Estimates are age adjusted to the 2000 U.S. standard population using five age groups: 18–44 years, 45–54 years, 55–64 years, 65–74 years, and 75 years and over.
Advance Data No. 382 + March 30, 2007 13

Table 4. Age-adjusted percents (with standard errors) of selected access to care and health care utilization characteristics among adults,

by presence or absence of serious psychological distress: United States, 2001–04

Psychological distress1

Serious psychological No serious psychological

distress distress

Standard Standard pCharacteristic Percent error Percent error value

Health insurance coverage:2

Private ........................................ 38.5 1.01 73.0 0.25 f

Medicaid/other public ............................... 25.0 0.95 5.7 0.11 f

Other ........................................ 7.7 0.51 2.7 0.08 f

Uninsured ...................................... 28.8 0.92 18.5 0.20 f

Have place to go when sick3 ............................ 82.4 0.70 85.3 0.16 f

Cannot afford:4

Mental health care................................. 18.1 0.72 1.5 0.04 f

Dental care ..................................... 32.2 0.88 9.6 0.12 f

Prescribed medicine................................ 31.9 0.90 6.6 0.09 f

Time since last talked to health professional:5

6 months or less ................................. 80.9 0.71 68.6 0.18 f

More than 6 months but not more than 1 year................ 7.4 0.47 14.0 0.13 f

More than 1 year.................................. 10.7 0.56 16.0 0.14 f

Never......................................... 1.0 0.18 1.4 0.06 –

Total number of doctor visits, past 12 months:6

None ......................................... 13.5 0.61 19.2 0.16 f

1–3 visits ...................................... 22.2 0.80 43.3 0.19 f

4–9 visits ...................................... 25.1 0.83 24.3 0.15 –

10 visits or more .................................. 39.2 0.90 13.2 0.13 f

Spoken to mental health professional, past 12 months ............ 32.4 0.86 5.3 0.08 f

f p<0.01 for a test of the difference between persons with serious psychological distress and no serious psychological distress.

– p≥0.01 for this test. 1

Six psychological distress questions are included in the the Sample Adult Core component. These questions ask how often a respondent experienced certain symptoms of psychological distress

during the past 30 days. The response code (0–4) of the six items for each person are summed to yield a scale with a 0–24 range. A value of 13 or more for this scale is used here to define

serious psychological distress. 2

Classification of health insurance coverage is based on a hierarchy of mutually exclusive categories. Persons with more than one type of health insurance were assigned to the first appropriate

category in the hierarchy. The category ‘‘Uninsured’’ includes persons who had no coverage as well as those who had only Indian Health Service coverage or had only a private plan that paid for

one type of service such as accidents or dental care. Health insurance coverage includes person under 65 years of age. 3

Have place to go when sick is based on a question in the survey that asked, ‘‘Is there a place that you usually go to when you are sick or need advice about your health?’’ 4

Cannot afford is based on a question in the survey that asked, ‘‘During the past 12 months, was there any time when you needed any of the following, but didn’t get it because you couldn’t afford

it?’’: Prescription medicine, Mental health care or counseling, Dental care (including check-ups). 5

Time since last talked to health professional is based on a question in the survey that asked respondents, ‘‘About how long has it been since you saw or talked to a doctor or other health care

professional about your own health?’’ These contacts may include office visits, hospital visits, home visits, and phone calls (but not calls made for arranging appoinments). 6

Number of doctor visits is based on a question in the survey that asked respondents, ‘‘During the past 12 months, how many times have you seen a doctor or other health care professional about

your own health at a doctor’s office, a clinic, or some other place?’’ Respondents are instructed to exclude overnight hospitalizations, visits to hospital emergency rooms, home visits, or telephone

calls.

NOTE: Estimates are age adjusted to the year 2000 projected U.S. population using five age group: 18–44 years, 45–54 years, 55–64 years, 65–74 years, and 75 years and over.
14 Advance Data No. 382 + March 30, 2007

Table 5. Age-adjusted percents (with standard errors) of adults aged 18 years and over with selected activity limitations and

impairments, by presence or absence of serious psychological distress: United States, 2001–04

Psychological distress1

Serious psychological No serious psychological

distress distress

Standard Standard pCharacteristic Percent error Percent error value

Impairment

Visual impairment................................... 27.4 0.86 8.6 0.11 f

Hearing impairment ................................. 8.1 0.47 3.0 0.06 f

Limitation

Activities of daily living (ADL)2 ........................... 9.8 0.52 1.4 0.04 f

Instrumental activities of daily living (IADL)3 .................. 19.3 0.70 3.2 0.06 f

Physical limitations

Difficulty walking 4 miles .............................. 41.1 0.87 9.7 0.11 f

Difficulty walking up 10 steps ........................... 35.3 0.86 7.3 0.10 f

Impairments in social functioning

Going out shopping, to movies, to sporting events4 .............. 33.7 0.91 4.9 0.08 f

Visiting friends, going to clubs, meetings, or parties5 ............. 31.8 0.90 3.7 0.07 f

Relaxing at home, reading, watching TV, sewing, or listening to music6 . 17.9 0.73 1.6 0.05 f

f p<0.01 for a test of the difference between persons with serious psychological distress and no serious psychological distress.

– p≥0.01 for this test. 1

Six psychological distress questions are included in the Sample Adult Core component. These questions ask how often a respondent experienced certain symptoms of psychological distress

during the past 30 days. The response code (0–4) of the six items for each person are summed to yield a scale with a 0–24 range. A value of 13 or more for this scale is used here to define

serious psychological distress. 2

Limitation in ADL is based on a question in the survey that asked respondents, ‘‘Because of a physical, mental, or emotional problem, [do/does] need the help of other persons with personal care

needs, such as eating, bathing, dressing, or getting around inside the home?’’ 3

Limitation in IADL is based on a question in the survey that asked respondents, ‘‘Because of a physical, mental, or emotional problem, [do/does] [person] need the help of other persons in

handling routine needs, such as everyday household chores, doing necessary business, shopping, or getting around for other purposes?’’ 4

Respondents were asked, ‘‘By yourself, and without using any special equipment, how difficult is it for you to: Go out to things like shopping, movies, or sporting events?’’ 5

Respondents were asked, ‘‘How difficult is it for you to: Participate in social activities such as visiting friends, attending clubs and meetings, going to parties. . .?’’ 6

Respondents were asked, ‘‘How difficult is it for you to: do things to relax at home or for leisure (reading, watching TV, sewing, listening to music)?’’

NOTE: Estimates are age adjusted to the year 2000 projected U.S. population using five age group: 18–44 years, 45–54 years, 55–64 years, 65–74 years, and 75 years and over.
Advance Data No. 382 + March 30, 2007 15

Table I. Completed interviews and response rates by year and for the 4 years combined: Technical Notes National Health Interview Survey, 2001–04

Sample design

The National Health Interview

Survey (NHIS) is a cross-sectional

household interview survey of the U.S.

civilian noninstitutionalized population.

Data are collected continuously

throughout the year in all 50 States and

the District of Columbia. The NHIS

Interviews and rates 2001 2002 2003 2004 2001–04

Completed interviews Number in thousands

Household .................... 38,932 36,161 35,921 36,579 147,593

Family ...................... 39,633 36,831 36,573 37,466 150,503

Sample adult .................. 33,326 31,044 30,852 31,326 126,548

Response rate Percent

Household .................... 88.9 89.6 89.2 86.9 88.6

Sample adult .................. 73.8 74.3 74.2 72.5 73.7

uses a multistage, clustered sample

design. Information on basic health

topics is collected for all household

members, by proxy from one family

member for adults not present at the

time of interview and by proxy for

children. Additional information is

collected for one randomly sampled

adult (the ‘‘sample adult’’) and one

randomly sampled child (the ‘‘sample

child’’) in each family with at least one

child. Self-response is required for the

Sample Adult questionnaire except in

the case of sample adults who are

physically or mentally incapable of

responding for themselves. An adult

family member who is knowledgeable

about the sample child’s health provides

information for the child component.

Interviews are conducted in the home

using a computer-assisted personal

interview (CAPI) questionnaire.

Telephone follow-up is permitted to

complete the survey after the initial

home interview if a further in-home

interview cannot be done.

Response rates

Combining years 2001–04, NHIS

interviews were completed for 147,593

households and 150,503 families, with

126,548 adults aged 18 years and over

completing the Sample Adult

questionnaire. The final response rate

for the 2001–04 combined household

files was 88.6% and for sample adult

files was 73.7%. Procedures used in

calculating response rates for combined

data years are described in detail in

Appendix I of the Survey Description of

the NHIS data files (61–64). The

number of completed household, family,

and sample adult interviews by year and

household and sample adult response

rates by year are presented in table I.

Age adjustment and

significance tests

Data shown in this report were age

adjusted using the 2000 projected U.S.

population (65–66). Age adjustment was

used to allow comparison among

population subgroups that have different

age structures. The following age groups

were used for age adjustment: 18–44

years, 45–54 years, 55–64 years, 65–74

years, and 75 years and over.

Estimates were calculated using

software for statistical analysis of

correlated data (SUDAAN) (23). The

SUDAAN procedure PROC DESCRIPT

was used to produce age-adjusted

percents and their standard errors.

Statistical tests performed to assess

the significance of differences between

estimates were two-tailed with no

formal adjustment for multiple

comparisons. The test statistic used to

determine statistical significance of the

difference between two percents was:

|Xa–Xb|

Z = . √Sa

2 + Sb2

Here Xa and Xb are the two percents

being compared, and Sa and Sb are the

SUDAAN-calculated standard errors of

the percents. The critical value used for

two-sided tests at the 0.01 level was

2.58.

Relative standard error

Estimates with a relative standard

error greater than 30% are considered

unreliable. The relative standard errors

are calculated as follows: Relative

standard error = (SE/Est)100, where SE

is the standard error of the estimate, and

Est is the estimate (percent, rate, mean,

or frequency). All estimates presented in

this report have a relative standard error

less than 30%.

Definitions of selected terms

Sociodemographic terms

Age—The age recorded for each

adult is the age at the last birthday. Age

is recorded in single years and grouped

using a variety of age categories

depending on the purpose of the table.

Education—The categories of

education are based on the years of

school completed or highest degree

obtained for persons aged 25 and over.

Only years completed in a school that

advances a person toward an elementary

or high school diploma, General

Educational Development high school

equivalency diploma (GED), college,

university, or professional degree are

included. Education in other schools and

home schooling are counted only if the

credits are accepted in a regular school

system.

Family income—Each member of a

family is classified according to the total

income of all family members. Family

members are all persons within the

household related to each other by

blood, marriage, cohabitation, or

adoption. The income recorded is the

total income received by all family

members in the previous calendar year.

Income from all sources includes wages,

salaries, military pay (when an armed

forces member lived in the family),

pensions, government payments, child

support/alimony, dividends, and help

from relatives. Unrelated individuals

living in the same household (for

example, roommates) are considered to

be separate families and are classified

according to their own incomes.
16 Advance Data No. 382 + March 30, 2007

Health insurance coverage—NHIS

respondents were asked about their

health insurance coverage at the time of

the interview. Respondents reported

whether they were covered by private

insurance (obtained from their employer

or workplace, purchased directly, or

through a local or community program),

Medicare, Medigap (supplemental

Medicare coverage), Medicaid, State

Children’s Health Insurance Plan

(SCHIP), Indian Health Service (IHS),

military coverage (including VA,

TRICARE, or CHAMP-VA), a Statesponsored health plan, another

government program and/or single

service plans. This information was used

to form a health insurance hierarchy for

persons under age 65 years.

For persons under 65 years of age,

a health insurance hierarchy of four

categories was developed. Persons with

more than one type of health insurance

were assigned to the first appropriate

category in the hierarchy listed below:

+ Private coverage—Includes persons

who had any comprehensive private

insurance plan (including health

maintenance organizations and

preferred provider organizations).

These plans include those obtained

through an employer, purchased

directly, or through local or

community programs.

+ Medicaid—Includes persons who do

not have private coverage, but who

have Medicaid and/or other Statesponsored health plans including

SCHIP.

+ Other coverage—Includes persons

who do not have private insurance or

Medicaid (other public coverage), but

who have any type of military health

plan (includes VA, TRICARE, and

CHAMP-VA) or Medicare. This

category also includes persons who

are covered by other government

programs.

+ Uninsured—Includes persons who

have not indicated that they are

covered at the time of the interview

under private health insurance (from

employer or workplace, purchased

directly, or through a State, local

government, or community program),

Medicare, Medicaid, SCHIP, a

State-sponsored health plan, other

government programs, or military

health plan (includes VA, TRICARE,

and CHAMP-VA). This category also

includes persons who are only

covered by IHS or only have a plan

that pays for one type of service such

as accidents or dental care.

Weighted frequencies indicate that

less than 1% of the adult population

under 65 years of age was ‘‘unknown’’

on health insurance.

Marital status—Respondents were

asked to choose a marital status

category. Adults could select the

category they felt most appropriate for

their marital situation. A legally

annulled marriage is considered as not

having taken place. Marital status is

classified into the following four

categories:

+ Married—This category includes all

persons who identify themselves as

married and who are not separated

from their spouses. Married persons

living apart because of circumstances

of their employment are considered

married. Persons may identify

themselves as married regardless of

the legal status of the marriage or sex

of the spouses.

+ Separated and divorced—This

category includes persons who are

legally separated from their spouse or

living apart for reasons of marital

discord, and those who are divorced.

+ Widowed—This category includes

persons who have lost their spouse

due to death.

+ Never married—This category

includes persons who were never

married.

Place of residence—Place of

residence in NHIS is classified as either

inside a metropolitan statistical area

(MSA) or outside an MSA. Place of

residence inside an MSA is further

subdivided as either central city or not

central city. Generally, an MSA consists

of a county or group of counties

containing at least one city (or twin

cities) having a population of 50,000 or

more plus adjacent counties that are

metropolitan in character and

economically and socially integrated

with the central city. In New England,

towns and cities rather than counties are

the units used in defining MSAs. There

is no limit to the number of adjacent

counties included in the MSA if they are

integrated with the central city, nor is an

MSA limited to a single State; MSA

boundaries may cross State lines.

Central city includes the largest city in a

metropolitan statistical area. One or two

additional cities may be secondary

central cities on the basis of either of

the following criteria: (a) the additional

city or cities must have a population

one-third or more of that of the largest

city and a minimum population of

25,000, or (b) the additional city or

cities must have at least 250,000

inhabitants. Noncentral city includes all

of the MSA that is not part of the

central city itself. Not MSA refers to

persons not living in an MSA.

Poverty status—Poverty status is

based on family income and family size

using the Census Bureau’s poverty

thresholds. ‘‘Poor’’ persons are defined

as persons whose family incomes are

below the poverty threshold. ‘‘Near

poor’’ persons have family incomes of

100% to less than 200% of the poverty

threshold. ‘‘Not poor’’ persons have

family incomes that are 200% of the

poverty threshold or greater.

Race—In this report, race and

ethnicity consists of four categories: not

Hispanic white, not Hispanic black or

African American, not Hispanic other

and Hispanic. Persons in these

categories are all single-race persons, in

accordance with the 1997 Office of

Management and Budget (OMB) federal

guidelines (67). Prior to 2003, ‘‘Other

race’’ was a separate race response on

the NHIS. In the 2003 NHIS, however,

editing procedures were changed to

maintain consistency with the U.S.

Census Bureau procedures for collecting

and editing data on race and ethnicity.

As a result of these changes, in cases

where ‘‘Other race’’ was mentioned

along with one or more OMB race

groups, the ‘‘Other race’’ response is

dropped, and the OMB race group

information is retained on the NHIS

data file. In cases where ‘‘Other race’’

was the only race response, it is treated

as missing and the race is imputed.

Although this change has resulted in an

increase in the number of persons in the

OMB race category ‘‘White’’ because
Advance Data No. 382 + March 30, 2007 17

this is numerically the largest group, the

change is not expected to have a

substantial effect on the estimates in this

report which categorizes persons by race

and ethnicity. Individuals who report

Hispanic ethnicity are categorized as

Hispanic regardless of their reported

race. The vast majority of persons

reporting ‘‘other race’’ are Hispanics.

More information about the race and

ethnicity editing procedures used by the

U.S. Census Bureau can be found at the

following web site: http://

www.census.gov/popest/archives/files/

MRSF-01-US1.html.

The text in this report uses shorter

versions of the new OMB race terms for

conciseness and the tables use the

complete terms. For example, the

category ‘‘Black or African American,

single race’’ in the tables is referred to

as ‘‘Black’’ in the text.

Terms related to health

characteristics and outcomes

Health status—Respondent-assessed

health status is obtained from a question

in the survey that asked respondents,

‘‘Would you say your health in general

was excellent, very good, good, fair, or

poor?’’ Information was obtained about

all respondents, with proxy responses

allowed for adults not taking part in the

interview.

Body mass index—Body mass index

(BMI) is calculated from the sample

adult’s responses to survey questions

regarding height and weight. BMI =

Weight (in kg)/[Height (in m2

)]. The

category Underweight is defined as a

BMI less than 18.5. Healthy weight is

defined as a BMI greater than or equal

to 18.5 and less than 25.0. Overweight

is defined as a BMI greater than or

equal to 25.0 and less than 30.0. Obese

is defined as a BMI greater than or

equal to 30.0.

Cigarette smoking status—

Information on cigarette smoking status

at the time of interview is derived from

two questions on the survey. All

respondents are first asked, ‘‘Have you

smoked at least 100 cigarettes in your

entire life?’’ Respondents who answered

‘‘yes’’ to the previous question are then

asked, ‘‘Do you now smoke cigarettes

every day, some days, or not at all?’’

+ Current smoker—There are two

categories of current smokers.

Persons in the first category smoke

every day, and persons in the second

category smoke only on some days.

+ Former smoker—This category

includes persons who have smoked at

least 100 cigarettes in their lifetime,

but currently do not smoke at all.

+ Never smoker—This category

includes persons who have never

smoked at least 100 cigarettes in their

lifetime.

Doctor or other health

professional—Doctor refers to medical

doctors (MDs) and osteopathic

physicians (DOs), including general

practitioners and all types of specialists

(such as surgeons, internists,

gynecologists, obstetricians,

proctologists, psychiatrists,

dermatologists, and ophthalmologists).

Other health care professional includes

physician assistants, psychologists,

nurses, physical therapists, chiropractors,

etc.

Number of visits to a doctor or

other health professional in the past 12

months—This is the number of visits to

a doctor’s office, clinic, or other place

that the respondent has made in the past

12 months regarding their own personal

health. Overnight hospital stays, hospital

emergency room visits, home visits, and

telephone calls are excluded.

Time since last physician or other

health care professional contact—This

is the length of time, prior to the week

of interview, since the respondent last

consulted a physician or other health

care professional in person or by

telephone for health treatment or advice

of any type. This may include a contact

while a patient is in the hospital as well

as a contact from a home visit. The

information for the time since the

sample adult last had contact with a

physician or other health care

professional is obtained from two

questions—one from the Family Core

and one from the Sample Adult Core. In

the Family Core the family respondent

is shown a calendar detailing the 2

weeks before the interview week and is

then asked the following question:

‘‘During those 2 weeks, did you

see a doctor or other health professional

at a doctor’s office, a clinic, an

emergency room, or some other place?’’

In the Sample Adult Core, the

respondent is asked: ‘‘About how long

has it been since you saw or talked to a

doctor or other health professional about

your own health?’’ The response

categories for this sample adult question

are: ‘‘6 months or less,’’ ‘‘more than 6

months, but not more than 1 year ago,’’

‘‘more than 1 year, but not more than 2

years ago,’’ ‘‘more than 2 years, but not

more than 5 years ago,’’ ‘‘more than 5

years ago,’’ and ‘‘never.’’ If the answer

to the Family Core question is ‘‘yes,’’

and if the person to whom the question

refers is the sample adult, then the

Sample Adult Core question is not

asked; rather, an implied response to the

Sample Adult Core question of ‘‘6

months or less’’ is recorded. If the

family respondent and the sample adult

were not the same person, and an

answer of ‘‘yes’’ was given to the

Family Core question, then the ‘‘6

months or less’’ implied response to the

Sample Adult question is proxy reported

(which occurs for approximately 4% of

sample adults).

Usual place of health care—Usual

place of health care was based on a

question that asked whether respondents

had a place that they usually went to

when they were sick or needed advice

about their health. If yes, they were

asked ‘‘What kind of place{is it/do you

go to most often}—a clinic, a doctor’s

office, an emergency room, or some

other place?’’ The choices for this

second question are: ‘‘clinic or health

center,’’ ‘‘doctor’s office or HMO,’’

‘‘hospital emergency room,’’ ‘‘hospital

outpatient department,’’ ‘‘some other

place,’’ or ‘‘doesn’t go to one place

most often.’’ Although ‘‘hospital

emergency room’’ is not considered a

‘‘usual place of health care’’ in other

publications, in this report it is. Also in

this report, persons who respond

‘‘doesn’t go to one place most often’’

are considered to have a place to go

when sick.

Visual impairment—Persons with

visual impairment are blind in one or

both eyes or report ‘‘trouble seeing,

even when wearing glasses or contact

lenses.’’
18 Advance Data No. 382 + March 30, 2007

Hearing impairment—Persons with

hearing impairment describe their

hearing without a hearing aid as ‘‘a lot

of trouble’’ or ‘‘deaf.’’

Limitation in ADL or IADL—

Limitation in ADL is based on a

question in the survey that asked

respondents, ‘‘Because of a physical,

mental, or emotional problem, [do/does]

[person] need the help of other persons

with personal care needs, such as eating,

bathing, dressing, or getting around

inside the home?’’ Limitation in IADL

is based on a question in the survey that

asked respondents, ‘‘Because of a

physical, mental, or emotional problem,

[do/does] [person] need the help of

other persons in handling routine needs,

such as everyday household chores,

doing necessary business, shopping, or

getting around for other purposes?’’

Physical limitations—Respondents

were asked, ‘‘By yourself, and without

using any special equipment, how

difficult is it for you to . . .

Walk a quarter of a mile— about

three city blocks?

Walk up 10 steps without resting?

The response categories were ‘‘not at all

difficult,’’ ‘‘only a little difficult,’’

‘‘somewhat difficult,’’ ‘‘very difficult,’’

and ‘‘can’t do at all.’’ Respondents were

considered limited if they answered

‘‘somewhat’’ or ‘‘very difficult’’ or

‘‘can’t do at all.’’

Impairments in social functioning—

Respondents were asked, ‘‘By yourself,

and without using any special

equipment, how difficult is it for you

to ...

Go out to things like shopping,

movies, or sporting events?

Participate in social activities such

as visiting friends, attending clubs and

meetings, going to parties . . .?

Do things to relax at home or for

leisure (reading, watching TV, sewing,

listening to music . . .)?

The response categories were ‘‘not

at all difficult,’’ ‘‘only a little difficult,’’

‘‘somewhat difficult,’’ ‘‘very difficult,’’

and ‘‘can’t do at all.’’ Respondents were

considered limited if they answered

‘‘somewhat’’ or ‘‘very difficult’’ or

‘‘can’t do at all.’’
20 Advance Data No. 382 + March 30, 2007

Suggested citation

Pratt LA, Dey AN, Cohen AJ. Characteristics

of adults with serious psychological distress as

measured by the K6 scale: United States,

2001–04. Advance data from vital and heatlh

statistics; no 382. Hyattsville, MD: National

Center for Health Statistics. 2007.

Copyright information

All material appearing in this report is in the

public domain and may be reproduced or

copied without permission; citation as to

source, however, is appreciated.

National Center for Health Statistics

Director

Edward J. Sondik, Ph.D.

Acting Co-Deputy Directors

Jennifer H. Madans, Ph.D.

Michael H. Sadagursky

U.S. DEPARTMENT OF

HEALTH & HUMAN SERVICES

Centers for Disease Control and Prevention

National Center for Health Statistics

3311 Toledo Road

Hyattsville, MD 20782

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07-0022 (3/07)

CS1094243

T27656

DHHS Publication No. (PHS) 2007-1250