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Survey Methodology
1. Introduction
Prior research has shown the
important role that transportation plays in linking persons with disabilities
to a range of community resources and services.[1]
Full participation in society, including school, work, and other activities,
requires access to effective modes of transportation for all persons,
especially those with a disability. Economic independence and self-sufficiency
are possible only when transportation is accessible, affordable, and available,
close to home and to the many destinations that people need to reach.[2]
As one of twelve operating
administrations within the U.S. Department of Transportation (DOT), the Bureau
of Transportation Statistics (BTS) has a compelling interest in the
transportation needs of persons with disabilities. One role of the BTS is to
provide transportation data to decision-makers and other stakeholders, and its
mission is to collect data, and compile, analyze, and publish statistics.
1.1 Goals of the Survey
In terms of national
transportation statistics, one area that suffers from a critical lack of
information is transportation use by persons with physical, mental or emotional
disabilities. Little is known about the ability of the nation’s transportation
system to fulfill the unique transportation needs of persons with disabilities.
For this reason, the BTS initiated the 2002 Transportation Availability and Use
Study to fill this information gap and allow the Government and other
researchers to analyze the data, report the results, and help provide an
informed basis for the development of transportation policies and programs.
In particular, the goals of the
survey are to:
- Identify the various modes of transportation used by persons with and without
a disability, including pedestrian walkways, automobiles, public transit, and
specialized transportation programs;
- Describe the levels of satisfaction and problems that persons experience
when using these travel modes;
- Permit comparisons of transportation use patterns, satisfaction levels,
and problems, between persons with and without a disability;
- Provide data on access to an automobile (including vehicles adapted for
use by persons with disabilities), driving behavior, accidents, and self-imposed
limitations on driving;
- Allow for the analysis of particular target groups of interest, such as
the elderly, low-income persons, working-age adults, and children with and
without disabilities; and
- As an overall goal, create an information resource for transportation planners
to use when developing national, state, and local policies and programs for
persons with disabilities.
According to the Census Bureau,
approximately 19 percent of the U.S.
resident (non-institutionalized) population age 5 and above have a disability.[3]
The disability prevalence rate among children under 5 years of age is
approximately 3 percent.[4]
In addition, analysis of the 1995 National Health Interview Survey on Disability
(NHIS‑D), using disability measures that were similar to the 2000 Census,
indicated that among households that report having persons with a disability,
79 percent contained only one person with disability, 18 percent contained two
persons with disability, and the remaining 3 percent contained three or more
persons with a disability.[5]
This information allowed the study team to estimate how many households would
need to be screened in order to locate one person with a disability for the
survey. Based on this analysis, approximately 30 percent of all households were
identified as having at least one person with a disability. Allowing for a 10
percent underreporting rate, the study team assumed a 27 percent rate when
estimating the required sample size for the survey (see Section 2.1, Sample
Design, below).
This study employed a screening
questionnaire, followed by an extended survey instrument for the selected
persons. Persons of any age (including children) were eligible to be
interviewed. Proxy interviews with a knowledgeable respondent were required for
persons under age 16 years and for persons who were unable to complete the
interview for themselves due to the severity of their impairments. The survey
employed data collection methods that ensured the greatest possible
participation regardless of the respondents' limitations. This included
Internet and mail versions of the questionnaire, a Spanish version of the
questionnaire, and the use of interpreters. The study was conducted by Westat,
a private survey research firm in Rockville, Maryland.
The survey gathered information in the following
topical areas:
- Frequency of travel outside the home, including trip purpose, mode of transportation,
frequency of use for different modes, need for assistance, and satisfaction
with transportation services;
- Availability of paratransit (door-to-door service) and respondent use of
paratransit;
- Personal motor vehicle ownership, use, and safety issues, including vehicles
modified for use by persons with disabilities;
- Experiences when using various modes of travel, including difficulties
with public and private transportation; and
- Respondent demographics (gender, age, income, ethnicity, race, disability,
living arrangements, employment status, school attendance, and education level).
The target for completed interviews
was 4,000 persons: 2,000 with disabilities and 2,000 without disabilities. The
study included both people with and without disabilities to allow comparisons
between the two groups for various transportation uses and problems, and to
determine which situations were unique to one group versus the other. With this
information, the BTS and others can make recommendations to improve
transportation for persons with disabilities.
The study actually completed 5,019 interviews, 2,321 with persons with disabilities
and 2,698 without. The data files and documentation include many different disability
measures, allowing analysts to construct their own definition of disability
using the multiple items in the survey. The disability questions were taken
from Census 2000 long form, as well as from the Americans with Disabilities
Act language, and a question on special education was added by the project team.
See the attached Computer Assisted Telephone Interviewing (CATI) questionnaire,
items B2a.-B2e., for the specific wording of these questions. For additional
information about the development of the Census disability questions, see the
following Web sites: http://www.ssa.gov/policy/docs/ssb/v62n4/v62n4p21.pdf,
and http://quickfacts.census.gov/qfd/meta/long_101608.htm.
1.2 Constructed Variables
The study team constructed a
separate variable, CDISABLD, that identified if a
respondent reported one or more of the several Census disabilities (questions
C3A-C4D). The purpose of this variable is to assist users who may want to
compare the results of this survey with Census 2000 data, according to a common
set of disability items. As a caveat, the 2000 Census collected disability
information from persons who were 5 years of age and older, while this survey
included persons of all ages. Therefore, when comparing the results of this
survey with the 2000 Census disability data, users should select only persons
who are 5 years of age or older.
In addition to the 2000
Census disability items, this survey asked two questions about a disability
related to the Americans Act (ADA) (questions B2a. and B2b.), and one question
about the receipt of special education services, which are designed for
children with disabilities (question C5.). A second constructed disability
variable, TDISABLD, identified if a respondent reported any of the ADA items, the special
education item, or the Census disability items. The purpose of this composite
measure is to give the user a variable that identifies respondents reporting
any of the disabilities in this survey.
Also, the "Other,
Specify" responses that could not be coded as an existing response item
were placed into newly constructed categories consistent with the new
information. Unique responses were left in the "Other" category. For
ease of identification, the new categories appear in the codebook below the
"Other" response. In addition,
a MODE variable was constructed to identify if the extended survey was
completed by CATI, Internet, or mail. There is a constructed age variable as
well (AGE) which reconciles any differences between the screener and the
extended reports of the respondent's age.
Sample weights were
developed for this data set, including the final full sample weight (RAKEDW00),
and 80 replicate weights (RAKEDW01-RAKEDW80), as described in Section 4., Weighting and Variance Estimation, below.
1.3 Caveats on the Interpretation of Data
The public use data file
consists of individual-level (person) records. For this reason, the counts
produced from this data set are person-level rather than household-level
figures. For example, the variable, TOTVEHI, identifies the number of household
vehicles. However, one may not sum this count to determine the total number of
vehicles in the country. This household vehicle count would require the use of
household weights, which are not available for the extended questionnaire
component of the survey. Only person weights are included in the file. Instead
of a vehicle count, one may count the number of persons who live in households
with a specified number of vehicles, (e.g., no vehicles, one vehicle, etc.).
Also, because this is a
person file, with only individual-level weights, many of the household-level
screener variables at the beginning of the survey are not applicable at the
person level and, therefore, do not appear in the
public use data file. This includes the two ADA disability questions (B2a.
and B2b). However, if either of these ADA items was the sole basis
for identifying a person with a disability for an extended interview, this was
reflected in the construction of the TDISABLD variable. A similar situation
occurred with the CDISABLD variable, where respondents were selected for an
extended disability survey based on a positive screener response to one or more
of the Census disability questions. The screener responses were used in these
cases because these Census items were missing from the extended interview file.
This occurred when there was a telephone disability screener response and a
mail extended interview, and the extended interview Census disability questions
were not answered by the respondent.
The
written documentation is organized according to the following sections:
- Introduction, including background information, study goals, and survey
content areas;
- Design and methods, including a description of the sample design, survey
operations, and quality control methods;
- Response rates; and
- Weighting and variance estimation.
The
documentation also includes:
The
codebook, listing the variables for the questions and response items;
Tables
of frequencies and percents with standard errors; and
Copies of the questionnaires, including the CATI, Internet and Mail
versions.
The accompanying CD includes the documentation and data files in SAS 8.0, SPSS
10, Excel, and comma-delimited ASCII formats.
[1] Burkhardt, J., et al. Mobility and Independence. Ecosometrics,
Inc., for the National Highway and Traffic Safety Administration and the U.S.
Department of Health and Human Services, Washington, DC, 1998.
[2] Kerschner, H, and Aizenberg, R. Supplemental Transportation
Programs for Seniors. The Beverly Foundation, Pasadena, CA. and the AAA
Foundation for Traffic Safety, Washington, DC, 2001.
[3] U.S. Census Bureau, Census 2000. Table DP-2. Profile of Selected
Social Characteristics: 2000.
[4] National Center for Health Statistics. Health United States,
2002. Hyattsville, MD: 2002.
[5] 1994/95 National Health Interview Survey on Disability, original
tabulations from public use data files.
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