Drivers survey ss Part B 100110rev

SUPPORTING STATEMENT
Drivers’ Awareness of and Response to Significant Weather Events and the Correlation of
Weather to Road Impacts
OMB CONTROL NO. 0648-xxxx
B. COLLECTIONS OF INFORMATION EMPLOYING STATISTICAL METHODS
1. Describe (including a numerical estimate) the potential respondent universe and any
sampling or other respondent selection method to be used. Data on the number of entities
(e.g. establishments, State and local governmental units, households, or persons) in the
universe and the corresponding sample are to be provided in tabular form. The tabulation
must also include expected response rates for the collection as a whole. If the collection has
been conducted before, provide the actual response rate achieved.
Random digit dialing (RDD) (home phones and cell phones) will be utilized to gather 1,200
responses from licensed drivers, following three winter storm events. The survey domain is
South Davis County, Salt Lake County, and Summit County, in Utah.
Pegus, the survey firm, was asked to draw a simple random sample from all exchanges in the
target area, and to conduct the interview in English. Pegus will provide 75% RDD sample
(nonautomated dialing system) and 25% cell phone sample (purchased cell phone numbers,
participants drawn randomly from the list of numbers).
There are several criteria for inclusion which will affect the population to which the data can be
generalized. The respondent (1) must be 18 years of age, (2) must not be driving at the time of
the interview (targeted for callback), (3) must have a current driver’s license for driving in Utah,
(4) reside in one of the target counties (South Davis, Salt Lake, or Summit), and (5) travel
regularly in the Salt Lake Valley (the area of interest to UDOT and NOAA). To increase validity
of responses, respondents who cannot remember if they did or did not travel in the Valley on the
day of the storm will be excluded.
The expected response rate, defined as the percentage of calls answered which result in
completion of the survey, will be between 20% and 25%. This is consistent with RDD surveys
of a similar length, conducted within the target area by PEGUS Research, during the past few
years. A large enough sample to result in 400 responses per storm will be purchased, taking into
account an expected 25 numbers dialed to result in each live contact, and at least four live
contacts made to result in one completed survey.
2. Describe the procedures for the collection, including: the statistical methodology for
stratification and sample selection; the estimation procedure; the degree of accuracy
needed for the purpose described in the justification; any unusual problems requiring
specialized sampling procedures; and any use of periodic (less frequent than annual) data
collection cycles to reduce burden.
More than 90% of Utah residents speak English. It is understood that there will be an
underestimation of responses from Spanish speaking drivers (drivers’ license exams are offered
only in English and Spanish). Using larger samples and fewer storms for greater precision with
our estimates was considered, but it was decided that a sample size of 400 for each survey would
1

be adequate for both point estimates and hypothesis testing (range within +/-5%), and that
obtaining information about 3 different storm events will offset the reduced precision.
3. Describe the methods used to maximize response rates and to deal with nonresponse.
The accuracy and reliability of the information collected must be shown to be adequate for
the intended uses. For collections based on sampling, a special justification must be
provided if they will not yield "reliable" data that can be generalized to the universe
studied.
It is understood that the quality of the sample is greatly influenced by the response rate. The
selected survey firm provides professional training, with an emphasis on interpersonal
communication, one factor in promoting a higher response rate. The interviewers will be asked
to call at different times during a 3-day period following the storm, so as to increase chances of
reaching the targeted respondents. There will be 5 call-backs, prior to excluding a telephone
number. One difficulty of this process is the short period of time in which to reach eligible
respondents. It was decided to contact people within 3 days, and no longer, to increase the
accuracy of their recollections, even though this limit has the potential to reduce the number of
surveys completed.
The relatively low response rate and lack of information about nonrespondents will not allow us
to make any claims that the responses will be representative of adult drivers in the three counties
targeted. We will compare the demographic information in the responses to known county
demographics; however, that will address only one aspect of nonresponse bias. However, we
believe that the information gathered will still be of use in our planning.
In any presentations or publications, we will stress that we cannot claim that the sample of those
who completed the survey is representative of the target population.
4. Describe any tests of procedures or methods to be undertaken. Tests are encouraged as
effective means to refine collections, but if ten or more test respondents are involved OMB
must give prior approval.
The survey was designed in a collaborative effort between NWS, UDOT, NWN, and the
University of Utah’s Department of Psychology. The final survey was developed using a series
of revisions based on interviews with colleagues. PEGUS Research, the survey firm, conducts
in-house tests of the computerized version, so it is not anticipated that these participants will be
contacted prior to the actual administration of the survey.
5. Provide the name and telephone number of individuals consulted on the statistical
aspects of the design, and the name of the agency unit, contractor(s), grantee(s), or other
person(s) who will actually collect and/or analyze the information for the agency.
The individuals listed below are the consultants for the statistical aspects of the design. As
indicated, Dawn Straatsma, PEGUS Research, will coordinate data collection, and Carol Werner,
University of Utah, will lead the analysis. The descriptive responses (weighted to represent the
population) will be provided by PEGUS Research. The actual analyses will be supervised by
Carol Werner, who will be examining relationships among variables, rather than a simple item
by item description.
2

Dawn Straatsma – Data Collection
PEGUS Research
801-990-6131
[email protected]
Carol Werner – Data Analysis
Department of Psychology
University of Utah
801.581.8938
[email protected]

3