Anonymity, confidentiality and privacy are 3 different but interrelated issues that need to be addressed in surveys. Anonymity requires that no personal identifiers are collected or retained; confidentiality is the assurance that there will be no disclosure of individually identifiable survey data to unauthorized persons; and privacy (as narrowly used here) addresses issues related to keeping other persons present at the time of the interview and/or the interviewer from knowing the respondent's answers. Privacy is addressed through different interviewing methods and is essentially a technical issue, whereas anonymity and confidentiality involve many aspects of survey design including sampling, data collection, data processing, data release and perception, both of respondents and the broader public. Because the NHSDA focuses largely on sensitive behaviors, it utilizes special procedures to enhance anonymity, confidentiality and privacy for respondents to maximize response rates and accuracy. Research shows that these procedures enhance accurate reporting. Modifications in these procedures could effect the quality of the sensitive drug use data. Confidentiality and privacy for sensitive data could be built into the NHIS procedures, but the level of anonymity would depend on how the NHIS and NHSDA were linked, i.e., anonymity is lost once the NHIS core sample person is used, because identifying information such as the social security number are collected in NHIS. A drug use supplement (using self-administered forms to enhance privacy) on the 1991 NHIS found lower rates of adult cocaine and marijuana use than the NHSDA and also achieved a lower response rate. This issue cannot be resolved based on available research. It requires new methodological research that would address the following, for example:
• The importance of anonymity, confidentiality and privacy are likely to be different and possibly reduced with computerized interviews. For example, a technique that uses tape recorders and/or computers to administer the survey [e.g., audio-CASI] could enhance privacy, probably beyond paper and pencil self-administration. NCHS is currently analyzing drug use data from a 1992 NHIS supplement that used an audio-cassette interview to assure privacy to adolescents and youth.
• The perception may be more important than the reality in the actual effect of anonymity and confidentiality on reporting of sensitive behavior. Do respondents know the difference between anonymity and confidentiality and do they really believe the assurances they are given? We may learn something about this by conducting a small study of NHSDA respondents, using a short post-interview form asking about respondents' perceptions of anonymity and confidentiality and how these perceptions impacted on their reporting of behaviors and their decision to participate in the survey. NCHS data are protected from disclosure by the strongest confidentiality laws of any federal statistical agency, but what does this mean to respondents. Current research at NCHS is investigating the perceptions of respondents about the confidentiality of data collected about other sensitive topics, abortion and sexual behaviors.
Many of the most important behaviors measured by the NHSDA have very low prevalence. To maximize precision, the NHSDA sample design incorporates stratification and varying sampling rates that target the sample toward high risk populations. The need for data on minorities also dictates oversampling. If the NHSDA is to continue to provide data with the current level of precision for rare drug using behaviors and for race/ethnic and other subpopulations, the NHSDA sampling plan will need to be maintained within the NHIS design. This raises the following:
• Coverage of hard-to-reach populations will need to be more of a concern in the NHIS than it is currently, because substance abuse estimates are probably more subject to coverage bias than are many of the health measures estimated by NHIS. This could influence how the NHIS field work is managed, both in terms of conducting interviews and controlling response rates, and the need for detailed data on the field experience. In addition, certain types of group quarters, such as shelters, are not currently included the NHIS sample frame.
• It may not be possible to use the screened NHIS households as the frame for the NHSDA, because the oversampling of Hispanics in the NHIS will likely "use up" all the screened Hispanic households that would be needed for the NHSDA. The only way to alleviate this would be to screen more households to accommodate NHSDA needs, resulting in additional costs. However, the current NHIS sample list was designed to support a sample 4 times the current planned sample size.
The ability to link the NHIS behavior, health status (especially mental health), and utilization data with the NHSDA would be extremely valuable. It would reduce overall respondent burden because the health and demographic items currently collected by the NHSDA could be dropped. Even without complete linkage of the samples at the household level, the use of the same PSUs or segments in both surveys would allow contextual analyses to be done using survey data. This linkage could also benefit small area estimation of substance abuse, such as is currently being done by SAMHSA. Nonresponse and coverage adjustments for the NHSDA could potentially be improved with the linkage of the NHIS with the NHSDA samples.
Several issues concerning the operation of the survey will need to be addressed.
• The timeliness of the data is a key issue. NHSDA estimates are regularly released within 6-7 months of completion of data collection. This schedule is important to White House Office of National Drug Control Policy. The ability to meet this schedule is based on an intensive field management and data management effort involving data editing, weighting, table production, and report writing by contractor and SAMHSA staff. If the NHIS and NHSDA are integrated, we will either have to maintain this capability or convince data users to adjust their data needs.
• The timeliness of responses to ad hoc requests for data from the NHSDA involves a similar situation. SAMHSA currently is able to address key policy issues related to substance abuse on a quick response basis using the NHSDA data files.
• The NHSDA is conducted under contract. Issues concerning access to confidential data by SAMHSA and the NHSDA contractor will need to be addressed.
The current NHSDA contract runs through 1996, and a new RFP to conduct the 1997-2000 surveys is in preparation and will soon be released. It is anticipated that the earliest any merging could be accomplished would be for the 1997 survey. However, given the timing of the RFP, there will be substantial issues concerning modification to this contract if major changes in the NHSDA are made.