Field Outcomes

Survey data collection by the Federal government requires prior approval by the Office of Management and Budget (OMB). Before submitting the formal request for data collection to OMB, NHTSA published a Notice in the Federal Register soliciting comments on the information collection. The Notice appeared in the Federal Register, 67:40, pages 9353-9354, February 28, 2002. No comments were received in response to the Notice. NHTSA then submitted the request for data collection to OMB. OMB approved the information collection on December 10, 2002, assigning it the OMB number 2127-0618 with an expiration date of December 31, 2003.

The field interviewing for the study commenced on January 8, 2003, following training of the field interviewers, and was completed on March 30, 2003. This was approximately the same length of field period as the 2000 Motor Vehicle Occupant Safety Survey (November 8, 2000 to January 21, 2001), the 1998 Motor Vehicle Occupant Safety Survey (November 8, 1998 to January 12, 1999), the 1996 Motor Vehicle Occupant Safety Survey (November 4, 1996 to January 5, 1997) and the 1994 Motor Vehicle Occupant Safety Survey (October 5, 1994 to December 11, 1994). However, the field period for the 2003 survey was moved to January to March in order to permit us to report results in the same calendar year as the data were collected. There was no reason to expect that the survey results would be affected by this change. Case status at the end of the field period was reported using the categories defined in Figure 4.

A total of 6180 interviews were conducted using Version 1, including 4677 for the cross-section and 1503 for the young adult over-sample. The average interview length for Version 1 was 21.7 minutes for the cross-section and 19.7 minutes for the over-sample. A total of 6197 interviews were completed using Version 2, including 4698 for the cross-section and 1499 for the young adult over-sample. The average interview length for Version 2 was 17.2 minutes for the cross-section and 17.8 minutes for the over-sample.

FIGURE 4 Sample Disposition Categories
NIS/DIS/Change #	The number was not in service, disconnected, or no longer an active number.
Non-residential	The number yielded a contact with a business, government agency, pay telephone, or other identifiable non-residential unit.
Computer/Fax	The number yielded an electronic tone indicating a fax machine or data line. A handful of other non-household numbers are included in this category.
Line problems	These represent dialing attempts that did not result in other standard outcomes and may be bad area codes, or other transient or permanent connection problems.
Probably unassigned	No answers, exclusively, were encountered on every contact over a period of several weeks until the study protocol (10 attempts) was reached.
Non-contact (max)	Answering machines or busy signals, as well as no answers, were encountered on all contact attempts until the study protocol (10 attempts) was reached.
No answer/busy	No household contact ever achieved, but less than 10 attempts. Ring, no answer or repeated busy signal on last attempt.
Answering machine	No household contact ever achieved, but less than 10 attempts. An answering machine was reached at the telephone number.
Language barrier	The interview could not be completed because of language barriers other than Spanish (which was treated as Spanish callback).
Health/Deaf	The designated respondent was unable to participate due to health or deafness.
Away for duration	The designated respondent was out of the area for the entire field period.
Screen-Outs	Households whose eligible participants did not meet the 16-39 age requirement in the over-sample version.
Quota Outs	Households whose eligible participants had met the gender by region quotas.
Callback	Contact was made with the household, but not necessarily the designated respondent
Refusal -- Initial	Someone in the household refused before selection of a designated respondent.
Refusal -- Second	Either an extremely strong initial refusal or a second refusal was encountered during refusal conversion, but before selection of a designated respondent.
Qualified Callback	The designated respondent had neither completed, nor refused an interview.
Refusal – Qualified	The designated respondent refused to participate in the survey.
Terminate	A respondent began the interview but refused to finish.
Complete	An interview was completed with the designated respondent.

For survey Version 1 Seat Belt Usage Issues, a total of 53,366 randomly selected telephone numbers were sampled within a geographically stratified national sampling frame for both sample components (the cross-section age 16 and older and the over-sample of persons age 16-39):

• 47% of the numbers were not active residential phone numbers, including 32% pre-screened or individually dialed Not-In-Service or Disconnected Numbers; 8% Business Numbers; and 6% computer, fax, cell phone or child phone lines;
• 17% of the numbers had reached the maximum number of contacts (10 attempts) and were still in no answer, answering machine or callback status, including 6% that were probably unassigned numbers because they were consistently no answers on all ten dialing attempts; and
• 1% were households in which the designated respondent was not interviewable (away for an extended period, incapacitated, or deaf) and an additional 1% were non-interviewable due to language barriers (non-Spanish).

At the close of the field period, only 1,675 cases (3%) were in callback status and an additional 1,460 cases (3%) were no answers or answering machines with less than 10 attempts.

The participation rate represents one of the most critical measures of potential sample bias because it indicates the degree of self-selection by potential respondents into or out of the survey. The participation rate is calculated as the number of completed interviews (including respondents who screen-out or quota out as ineligible) divided by the combined total number of completed interviews, terminated interviews, and refusals to interview. The participation rate for Version 1 is based on the following elements:

• 6,180 completed interviews;
• 510 cases in which someone in the household completed the household screen, but no one in the household was interviewed because the quota for that region or gender had already been filled;
• 5,321 cases in which someone in the household completed the household screen, but no one in the household was found to be eligible for the full interview because of age-related screen-outs among the age 16-39 over-sample; and
• 3,131 refusals to be interviewed (including 1,610 second or hard refusals and 119 terminated interviews).

Based on the standard calculations of participation rate, the participation rate for Version 1 was 79.3%. The response rate³ (40.0%) was lower because it included all presumed eligible households in the denominator. Response rate was a measure of sample coverage. The Final Summary Disposition of the Version 1 sample is given in Table 3. The table includes breakouts for each survey component (national cross-section and the age 16-39 over-sample).

TABLE 3 Sample Disposition - Version 1, Seat Belt Usage Issues: 2003
Version 1, 2003		CROSS-SECTION	OVER-SAMPLE	TOTAL
T	TOTAL	29544	23822	53366
A1	NON-ELIGIBLE HOUSEHOLD	13878	11027	24905
A	NIS/DIS/Change#/Intercepts	9648	7664	17312
A	Non-residential #	2367	1792	4159
A	Computer/Fax tone	1672	1405	3077
A	Line problem	191	166	357
B1	UNKNOWN ELIGIBLE HOUSEHOLD	3397	2588	5985
B	Probable unassigned number (10 attempts)	1786	1487	3273
B	Non-contact (10 attempts)	710	542	1252
B	No answer/Busy (less than max attempts)	569	318	887
B	Answering machine (less than max attempts)	332	241	573
C1	NOT ELIGIBLE REPONDENT	1134	5584	6718
C	Language barrier	231	135	366
C	Health/Deaf	344	93	437
C	Respondent away for duration	49	35	84
C	Screen-out (No aged 16-39)	0	5321	5321
C	Quota-out (gender/region quota)	510	0	510
D1	UNKNOWN ELIGIBLE RESPONDENT	5699	2846	8545
D	Callback (10 attempts)	3094	1678	4772
D	Callback (less than max attempts)	773	241	1014
D	Spanish Callback not screened	106	55	161
D	Refusals – Initial	693	295	988
D	Refusals – Second/Hard	1033	577	1610
E1	QUALIFIED NON-COMPLETE	759	274	1033
E	Qualified callback	385	115	500
E	Refusals – Qualified	290	124	414
E	Terminates	84	35	119
F	COMPLETE	4677	1503	6180
F	Total Completes	4677	1503	6180
A'	ELIGIBLE HH=C+D+E+F/A+C+D+E+F	46.9%	48.1%
B'	ESTIMATED QUALIFIED HH=B * A'	1594	1244	2838
C'	ELIGIBLE RESPONDENTS=E+F/C+E+F	82.7%	24.1%
D'	ESTIMATED ELIGIBLE RESPONDENTS=D * C'	4715	687	5402
	AAPOR RESPONSE RATE 3=F/(F+E+B'+D')	39.8%	40.5%	40.0%
	Participation Rate	71.2%	86.9%	79.3%

For survey Version 2 Child Safety Seat Issues, a total of 44,327 randomly selected telephone numbers were sampled within a geographically stratified national sampling frame for both sample components (the cross-section age 16 and older and the over-sample of persons age 16-39):

• 47% of the numbers were not active residential phone numbers, including 33% pre-screened or individually dialed not-in-service or disconnected numbers; 8% business numbers; and 6% computer, fax, cell phone, or child phone lines;
• 12% of the numbers had reached the maximum number of contacts (10 attempts) and were still in no answer, answering machine or callback status, including 2% that were probably unassigned numbers because they were consistently no answers on all ten dialing attempts; and
• 1% were households in which the designated respondent was not interviewable (not available, away for an extended period, incapacitated, or deaf) and an additional 1% were non-interviewable due to language barriers (non-Spanish).

At the close of the field period, only 1,314 cases (3%) were in callback status and an additional 3,546 cases (8%) were no answers or answering machines with less than 10 attempts.

The participation rate for Version 2 is based on the following elements:

• 6,197 completed interviews;
• 245 cases in which someone in the household completed the household screen, but no one in the household was interviewed because the quota for that region or gender had already been filled;
• 3,894 cases in which someone in the household completed the household screen, but no one in the household was found to be eligible for the full interview because of age-related screen-outs among the age 16-39 over-sample; and
• 2,658 refusals to be interviewed (including 1,280 second or hard refusals and 196 terminated interviews).

Based on the standard calculations of participation rate, the participation rate for Version 2 was 79.5 percent. The response⁴ rate (44.9%) was lower because it included all presumed eligible households in the denominator. Response rate was a measure of sample coverage. The Final Summary Disposition of the Version 2 sample is given in Table 4, on the next page. The table includes breakouts for each survey component (national cross-section and the age 16-39 over-sample).

TABLE 4 Sample Disposition - Version 2, Child Safety Seat Issues: 2003
Version 2, 2003		CROSS-SECTION	OVER-SAMPLE	TOTAL
T	TOTAL	25643	18676	44319
A1	NON-ELIGIBLE HOUSEHOLD	11828	8960	20788
A	NIS/DIS/Change#/Intercepts	8333	6260	14593
A	Non-residential #	1921	1586	3507
A	Computer/Fax tone	1489	1081	2570
A	Line problem	85	33	118
B1	UNKNOWN ELIGIBLE HOUSEHOLD	4106	1744	5850
B	Probable unassigned number (10 attempts)	215	859	1074
B	Non-contact (10 attempts)	401	829	1230
B	No answer/Busy (less than max attempts)	2432	39	2471
B	Answering machine (less than max attempts)	1058	17	1075
C1	NOT ELIGIBLE REPONDENT	606	4056	4662
C	Language barriers	194	107	301
C	Health/Deaf	143	40	183
C	Respondent away for duration	24	15	39
C	Screen-out (No aged 16-39)	0	3894	3894
C	Quota-out (gender/region quota)	245	0	245
D1	UNKNOWN ELIGIBLE RESPONDENT	3661	2185	5846
D	Callback (10 attempts)	1590	1260	2850
D	Callback (less than max attempts)	783	51	834
D	Spanish Callback not screened	44	53	97
D	Refusals - Initial	467	318	785
D	Refusals – Second/Hard	777	503	1280
E1	QUALIFIED NON-COMPLETE	744	232	976
E	Qualified callback	311	72	383
E	Refusals - Qualified	290	107	397
E	Terminates	143	53	196
F	COMPLETE	4698	1499	6197
F	Total Completes	4698	1499	6197
A'	ELIGIBLE HH=C+D+E+F/A+C+D+E+F	45.1%	47.1%
B'	ESTIMATED QUALIFIED HH=B * A'	1851	821	2672
C'	ELIGIBLE RESPONDENTS=E+F/C+E+F	90.0%	29.9%
D'	ESTIMATED ELIGIBLE RESPONDENTS= D * C'	3294	654	3948
	AAPOR RESPONSE RATE 3=F/(F+E+B'+D')	44.4%	46.8%	44.9%
	Participation Rate	74.7%	84.6%	79.5%

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³Response Rate 3 (RR3) from the American Association for Public Opinion Research, Standard Definitions: Final Dispositions of Case Codes and Outcome Rates for Surveys, 2004, was used as the basis for this calculation.

⁴Response Rate 3 (RR3) from the American Association for Public Opinion Research’s Standard Definitions: Final Dispositions of Case Codes and Outcome Rates for Surveys, 2004, was used as the basis for this calculation.