Omnibus Survey
Household Survey Results
Month Specific Information
May 2002

This report presents the results of the May 2002 Household Survey. Each monthly survey will contain a set of core questions that are based on critical information needs within DOT. In addition, supplemental questions will be included each month that correspond to one of DOT's five strategic goals: safety, mobility, economic growth, human and natural environment, and security. Finally, specific questions posed by the various DOT modes will be included in each survey and will vary from month to month.

The May 2002 survey collected data from May 4, 2002 through May 15, 2002. Data were collected from households in the U.S. using a Random-Digit-Dialed telephone methodology. The final completed sample size is 1,015 cases, and the total number of variables in the public-use dataset is 163. The data were collected by M. Davis and Company, under contract with the BTS.

Sample Telephone Number Selection

There were 8,200 telephone numbers purchased for the May 2002 survey. A total of 5,061 of these numbers were identified as working residential numbers and were divided into 67 replicates. Each of the 34 fielding replicates released initially contained approximately 100 households. Eleven additional replicates were released during fielding containing approximately 50 households each. Eight unused replicates from May's sample were used to conduct a pretest. Each pretest replicate had approximately 50 households. Fourteen of the 67 May replicates were not utilized in the actual interviewing. Hence, 3,955 numbers were released for use by the telephone interviewers. For this survey, the total number of telephone numbers in the sampling frame, N, is 261,905,600. The total number of telephone numbers in the sample (numbers dialed) is 3,871.

Specific Weight Adjustment for Households with Multiple Telephone Numbers

Some households have multiple telephone lines for voice communication.

The table below provides summary statistics for the number of telephone lines in the monthly sampled households.

Table 1: Number of Telephone Lines per Household

Specific Weight Adjustment for Number of Eligible Household Members

The probability of selecting an individual respondent depends upon the number of eligible respondents in the household. The table below provides summary statistics for the number of eligible members in the monthly sampled households.

Table 2: Number of Eligible Household Members

Post-Stratification Weight Adjustments

Adjusting weighted survey counts so that they agree with population counts provided by the Census Bureau can compensate for different response rates by demographic subgroups, increase the precision of survey estimates, and reduce the bias present in the estimates resulting from the inclusion of only telephone households.

The cells, used to construct post-stratification adjustments for this month, together with the number of sample observations and the national population estimates from the Census Bureau are shown in the table below.

Table 3: Post-Stratification Cells

Data Collection Schedule

The survey period was twelve days, from May 4 through May 15. Interviewers did not work Sunday May 12 as it was Mother's Day. In addition, there was an eleventh day of interviewing in May 2000 in order to achieve the 1,000-interview minimum. A total of 1,015 interviews were completed during the survey period.

Disposition of Sample Telephone Numbers

The table below presents the distribution of household telephone numbers by disposition categories. The number of household cases in each category was then used to calculate a CASRO response rate of approximately 37 percent.

Table 4: Distribution of Household Cases by Disposition