THE SURVEY SAMPLE
We drew our sample from records of Army, Air Force, Marine Corps, and Navy personnel who were reported to have served in ODS/DS between August 1, 1990, and July 31, 1991. We focused on the subset of personnel who served on the ground (as opposed to personnel who were located at sea in the Persian Gulf or who only flew over the area) in the KTO. Personnel who were ultimately eligible to be surveyed consisted of:
The sample was stratified by branch of service, occupational specialty, rank, and unit location. We stratified in these dimensions to (1) achieve equal precision in the estimates across services, and (2) to interview sufficient numbers of personnel with special knowledge or special living conditions. In particular:
We conducted an extensive literature review of other retrospective studies to evaluate survey methods used to reduce recall bias. This review and its findings, in combination with the insight gained from our initial pretests, guided the survey's final organization and grouping of topics. Table 2.1 outlines the instrument. Appendix A provides additional details about the survey instrument design process, and Appendix D provides additional details and a complete discussion of the recall bias results.
Module I: Introduction and Screener|
Informed consent, privacy statement, and confidentiality pledge
Assessment of general awareness of Gulf War issues to measure recall bias
Module II: One Month in the Persian Gulf
Module III: Pest Problems and Pesticide Use
Module IV: Background Questions
The survey was designed to be completed in 30 minutes on average. To achieve this, we had to make a tradeoff between collecting detailed data for a specific, short time frame or collecting more general data about the respondent's entire ODS/DS experience. To collect the most information possible that still allowed extrapolation to the entire ODS/DS period, we chose to select one month at random out of each respondent's tour, creating a cumulative database of detailed information across respondent experiences.
We specifically organized the instrument to trigger memories of the time period by asking respondents first to visualize their location during the randomly selected month, then by asking specific questions regarding their living quarters, bathroom facilities, eating arrangements, and work areas. Not only was this preliminary information of interest to us in our analysis, but it also served to set the scene for respondents, preparing them for the more detailed questions regarding their pesticide use by setting up the contextual memory on which they could draw at the outset of the interview.
Using primarily the feedback of pretest respondents, we organized the questions so that information was first collected on the various pesticide forms used. We then asked specific questions addressing each form indicated by the respondent. Personal and field-use pesticides were queried separately in this same format. This approach paralleled the way respondents recollected their use of pesticides: First the various products were listed, then each type and its use were described.
The list of possible smells was constructed by including all the smells that characterize the different pesticides shown in Table 2.2. These were cooking oil, rotten eggs or sulfur, gasoline, insecticide, kerosene, chemical, sweet, and musty. Similarly, the colors were defined as colorless/clear, light brown, dark brown, gray, orange, red, white, opaque/cloudy/milky, and yellow. Both color and smell allowed the respondent to choose multiples and to add other comments. The combination of form, color, smell, and the location where the pesticide was used can often be used to specify a unique active ingredient.
We separately grouped the possible uses of pesticides into those for personal use and those for field use. Personal-use pesticides were defined as those used directly on the skin or uniform by the respondent. For field-use pesticides, the user could have been either the respondent or another individual observed by the respondent.
The specific pesticides used by or near the respondent depended on the type of location where she/he spent most of the time during the period in question and on the type of pests present. Some pesticides were used only indoors, others only outdoors, others in latrines, etc. Some were used on the skin and others on uniforms or netting only.
We divided the types of geographical locations where people spent most time while in the Persian Gulf into the following categories:
|Situation Type||Possible Pesticides Used|
|Sleeping or working areas|
|Building or warehouse||Allethrin/permethrin/resmethrin, azamethiphos, cypermethrin, deltamethrin, dichlorvos, diphacinone, methomyl, d-phenothrin|
|Tent||Allethrin/permethrin/resmethrin, azamethiphos, dichlorvos, diphacinone, methomyl, d-phenothrin, valone|
|Military vehicle||Azamethiphos, diphacinone, methomyl, valone|
|Outdoors||Aluminum phosphide, azamethiphos, B.T., carbaryl, cypermethrin, deltamethrin, diazinon, lindane, malathion, methomyl, parathion, propoxur, pyrethrin, valone|
|Mess hall/eating area||Allethrin/permethrin/ resmethrin, azamethiphos, chlorpyrifos, diazinon, dichlorvos, diphacinone, malathion, methomyl, d-phenothrin, propoxur, valone|
|Latrine||Azamethiphos, chlorpyrifos, dichlorvos, diazinon, malathion, methomyl, d-phenothrin, propoxur, valone|
For each pesticide used by the respondent, we asked questions about where it was obtained, its frequency of use, and, if they stopped using it, the reason. For the nonliquid/nonspray pesticides, we also recorded information on disposal.
For the field use of sprays, we recorded information on the type of sprayer used (hand-held, truck, or plane fogger) as well as the areas sprayed (indoors, outdoors, outside the camp perimeter, and specific areas inside the camp).
Advance Recall Aids
We sent a letter to each respondent in advance of the interview explaining the study's purpose, its sponsor, and what the interview would be covering. We also enclosed a brochure with answers to frequently asked questions and materials we developed to aid recall. These materials included a map of the Persian Gulf, a calendar with key events highlighted for the months August 1990 through July 1991--key events that respondents could use to bound experiences during their tour--and a Gulf War Service Fact Sheet (mimicking questions from Module I) to be filled out in advance of the interview. This fact sheet, in addition to the other materials, was intended to initiate recall of the respondent's tour in advance of the interview.
Assessing Recall Bias Through Re-Survey
We also randomly selected a subset of 8 percent of the respondents who agreed to be reinterviewed with selected questions from the original survey to assess the reliability of answers about exposure to pesticides during ODS/DS. We administered the second survey after about six weeks, during which time respondents were generally expected to forget, at least in part, how they had answered the first survey. In this way, we were able to examine what fraction of their answers changed. The interpretation of this change can be ambiguous, but re-testing helped us to assess how reliable the answers were over time.
We administered the recall survey to a random subsample of the original respondents. We re-asked the location and timeline questions to reestablish context, and then asked about the types of personal and field uses of pesticides respondents participated in or observed. If they indicated a pesticide type that matched something they listed the first time, we continued with the more detailed questions about names, sources, and frequency of use. (If there was no match, we had no data to compare against and so did not collect additional information.)
In addition, once the study was under way, an interviewer specialist was trained in refusal conversion. This person followed up with all respondents who had previously refused participation, in an effort to better inform them of the nature of the project and give them another chance to participate. Of those recontacted, approximately 70 percent agreed to the interview.
Response and nonresponse rates are summarized in Table 2.3. The interviewers were able to contact 76 percent of the personnel in the initial sample. Interviews were completed for 2,005 out of the original 3,264 personnel selected.
Survey Response Rates
|Response Status||Percentage of Subgroup||Percentage of Sample|
|Respondent not in Gulf War||7|
|Respondent located, no interview|
|Unable to respond||2|
|Respondent not located|
NOTE: The original sample size was 3,264.
In all, only 3 percent of the sampling frame refused to participate, or about 4 percent of those contacted. Two percent were deceased or not able to respond--deployed active duty personnel, for example, often could not respond. Another 7 percent of the personnel in the sampling frame were actually reached but indicated that they had not served in ODS/DS.
As we anticipated, the most common reason for nonresponse was an inability to locate the individual. A detailed and disciplined approach was undertaken to find as many personnel in the sampling frame as possible. However, in spite of these efforts, 23 percent could not be located before the conclusion of the interview period. Individuals who were in the Air Force during ODS/DS were easier to locate than those in the other services. Retired personnel were easier to locate than personnel still on active duty or in the reserves, and civilians were harder to locate. Finally, minorities and females were more difficult to locate than white males.
Sample and Population Demographics
(n = 2,005)
(n = 469,047)
|E-1 to E-3||14.4||16.6|
|E-4 to E-5||44.0||54.1|
|E-6 to E-9||30.7||17.8|
NOTE: Totals may not sum to 100 percent because of rounding.
An analysis of those who said that they were not in ODS/DS shows that: (1) junior enlisted and female personnel (in the database) were less likely to have served in ODS/DS, and (2) personnel who were located in urban areas or had food service occupations were more likely to have been correctly listed as being in ODS/DS.
Coast Guard personnel were also included in the sampling frame and two members of the Coast Guard were actually surveyed. (Five were originally selected to be interviewed. Of these, two were located and interviewed, two more were located but did not meet the survey eligibility criteria, and one could not be located.) Their results are not included in the tabulations because the results could not be generalized to the Coast Guard population on the ground, in theater. However, we carefully read these respondents' responses individually and found nothing unusual. These two personnel used typical pesticides in typical ways with typical frequency.
We did not oversample preventive medicine personnel, who have had special training and have knowledge of pesticides, as they had been previously separately interviewed by OSAGWI.
Colors and smells were derived from NIOSH (1997); the Merck Index, 12th edition; Hazardous Substances Data Bank (HSDB) (sponsored by the National Academy of Medicine); and Toxicological Data Network (TOXLINE) (sponsored by the National Academy of Medicine).
Although the best information available indicates that aerial spraying was never authorized or used, we included the category for completeness and as an external validation of official reports.
Examples of these materials can be found in Spektor et al. (forthcoming).
More precisely, we administered the recall survey to a random subset of those who agreed to be recontacted. However, 97.4 percent of those surveyed the first time agreed to be recontacted.
The population error rate differs from the sample error rate of 7 percent (Table 2.3) because of weighting. The difference occurs because the sample respondents who did not serve had higher weights than those who did; hence the population percentage is larger than the sample percentage.
Also, note that this 12 percent error rate does not capture the reverse type of error: personnel who served in the Gulf War but are not in the Gulf War database. From our survey, we have no way of quantifying this type of error.