Behind the Numbers: SAMHSA's Survey on Drug Use
By Rebecca A. Clay
"Watch out for the polar bear!" is not the kind of advice
most people expect to hear while they're on the job. For Peter H.
Law, however, the threat of a face-to-face encounter with a bear
was just one of the hazards he confronted while collecting information
about substance use and mental illness in isolated Alaskan villages.
In Alaska, data collection can take place
in a snow-covered igloo-shaped building. (Photo
by Peter Law)
As an interviewer for SAMHSA's National Survey on Drug Use and
Health, Mr. Law traveled by helicopter through dense fog to get
to one village and through a blizzard to reach another one. He tells
the story of one remote town where he inched along narrow icy paths,
with chained dogs lunging at him on one side and a steep drop-off
on the other. At one point, he crawled on his hands and knees to
get to a house raised on stilts high on a hillside.
Travel to and from Alaska's isolated villages
is usually by helicopter. (Photo by
"I felt like Indiana Jones," said Mr. Law. "What
would probably be the trip of a lifetime for someone else is just
another day at work for an interviewer in Alaska."
Each year, field interviewers like Mr. Law fan out across the
Nation to knock on thousands of doors and collect information on
residents' alcohol, tobacco, and illegal drug use. Formerly known
as the National Household Survey on Drug Abuse, the National Survey
on Drug Use and Health is the Federal Government's leading source
of statistical data on the prevalence, patterns, and consequences
of alcohol, tobacco, and illegal drug use among the civilian, non-institutionalized
U.S. population age 12 and older.
The survey also collects information about mental illness and mental
health treatment. SAMHSA's Office of Applied Studies (OAS) plans
and manages the survey, which is conducted by a not-for-profit research
organization, RTI International, in North Carolina.
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A Massive Effort
Data are collected in urban areas similar
to this Philadelphia neighborhood. (Photo
by Erin J. Pond)
Initiated in 1971 in response to growing concerns about substance
abuse, the survey took place approximately every 2 years in its
early days. When demand for up-to-date information increased in
the late 1980s, the survey became an annual undertaking.
Another inner-city street scene. (Photo
by Erin J. Pond)
Today, the survey relies on more than 700 field interviewers to
administer questionnaires during face-to-face interviews at the
homes of a sample representing 98 percent of the U.S. population.
In 2002, field interviewers collected data from 68,126 people in
houses, apartment buildings, homeless shelters, dormitories, rooming
houses, migrant worker camps, halfway houses, and civilian quarters
on military bases in all 50 states and Washington, DC. The survey
excludes active-duty military personnel, homeless persons who do
not use shelters, inmates at correctional facilities, and people
in nursing homes, mental institutions, and long-term hospitals.
Philadelphia's urban landscape. (Photo
by Erin J. Pond)
This massive effort produces a wealth of information, said Joseph
C. Gfroerer, Director of the Division of Population Surveys within
"Policymakers, researchers, service providers, and others
all turn to the survey results to inform their work," said
Mr. Gfroerer. "The survey provides crucial information about
the extent of substance use as well as the unmet need for prevention
Because of shifting information needs and other key factors, the
survey is constantly evolving. Some of the survey's changes reflect
changes in types of drug use. The current survey asks about Ecstasy,
a "club drug" often used by teenagers at late-night dances,
for example. Two decades ago, most people had not heard of this
drug, and it was not included in the survey. Other changes reflect
new demographic realities. In 1999, for instance, the survey revised
its questions about racial and ethnic background to better reflect
the Nation's diversity.
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The sheer size of this nationwide effort makes the survey a challenge.
And it can be difficult to persuade people to participate.
"Most people wouldn't respond positively to someone saying,
‘I'm here from the Government, and I want to ask you about
your drug use,' " said Mr. Gfroerer. "But once people
understand the purpose of the survey, and hear from our highly trained
interviewers how data are collected and handled, they're usually
willing to help." About 80 percent of those asked to participate
actually complete the interview.
In the field, interviewers don't just decide at random which doorsteps
to approach. Using statistical techniques, survey designers first
compile a sample of more than 175,000 addresses and then narrow
it down to eligible ones. Potential respondents in those households
receive an introductory letter explaining the survey and all confidentiality
Interviewers then head out to each location or home, using small,
hand-held computers to collect basic demographic information about
household members. The computer uses that preliminary information
to select appropriate survey participants. Those who complete the
interview receive a $30 payment as a thank-you.
To collect basic demographic information, interviewers use laptop
computers. They read questions from their screens and then type
responses into their keyboards. For more sensitive questions, interviewers
offer their computers to respondents for privacy. Respondents can
read the questions on screen or listen with headphones, and then
they key their responses into the laptop. The entire process takes
about an hour.
"These computer-assisted, self-interviewing techniques are
designed to give respondents a very private way of answering questions,"
said Mr. Gfroerer. "That increases the chances that they'll
be honest when they're detailing any illicit drug use and other
sensitive behaviors." In fact, he pointed out, research shows
that such techniques produce more honest answers than pencil-and-paper
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A Wealth of Information
At the end of each day, interviewers transmit data collections
electronically to RTI International by phone.
Once the raw data are received, computers perform complex editing
procedures and check for consistency of reporting. For example,
the computers may find a missing or ambiguous answer in response
to a question about most recent drug use. Rather than "in the
past 30 days" or "more than 12 months ago," the respondent
answered with a vague "some point in lifetime." In that
case, a process called imputation fills in the response that statistical
models deem most likely to be correct.
The process assembles and taps into a set of respondents with
complete data, similar to the respondent in question. The computers
choose one respondent at random and then borrow his or her "good"
answer to fill in the missing response.
The final step is the calculation of analysis weights. This step
is designed to ensure that the data set is truly representative
of the U.S. population as a whole. The survey intentionally samples
a disproportionate number of young people, Mr. Gfroerer explained;
to account for that oversampling, the survey assigns different weights
to respondents. These adjustments help avoid skewed results.
The calculation of analysis weights also considers possible variations
in participation rates in certain geographic areas and other key
factors that could produce unrepresentative results.
Many publications are generated from this effort. The primary
from the 2002 National Survey on Drug Use and Health: National Findings,
more than 250 pages, provides a comprehensive summary of the latest
A companion report, Overview of Findings
from the 2002 National Survey on Drug Use and Health, offers
a summary version with highlights of the most important findings
and a brief discussion of methodological issues. OAS also produces
specialized "short reports" on specific populations, age
groups, and topics of interest.
For copies of the reports, contact SAMHSA's National Clearinghouse
for Alcohol and Drug Information at P.O. Box 2345, Rockville, MD
20847-2345. Telephone: 1 (800) 729-6686 (English and Spanish) or
1 (800) 487-4889 (TDD). Publications can also be viewed on the SAMHSA
Web site at www.oas.samhsa.gov.
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