Several researchers have begun this effort already. The post-survey adjustment methods applied to non-probability sampling have largely mirrored efforts in probability samples. Although this may be appropriate and effective to some extent, further consideration of selection bias mechanisms may be needed. We believe an agenda for advancing a method must include these attributes.

Public reporting burden for the collection of information is estimated to average 1 hour per response, including the time for reviewing instructions, searching existing data sources, gathering and maintaining the data needed, and completing and reviewing the collection of information. Send comments regarding this burden estimate or any other aspect of this collection of information, including suggestions for reducing this burden, to Washington Headquarters Services, Directorate for Information Operations and Reports, 1215 Jefferson Davis Highway, Suite 1204, Arlington VA 22202-4302. Respondents should be aware that notwithstanding any other provision of law, no person shall be subject to a penalty for failing to comply with a collection of information if it does not display a currently valid OMB control number. The survey is the eighth in a series of DoD surveys conducted since 1980 and has three broad aims: (a) to continue the survey of substance use among active-duty military personnel, (b) to assess progress toward selected Healthy People 2000 objectives for active-duty military personnel, and (c) to provide baseline data regarding progress toward selected Healthy People 2010 objectives for active-duty military personnel. As such, it provides comprehensive and detailed estimates of the prevalence of alcohol, illicit drug, and tobacco use and the negative effects of alcohol use. In combination with data from the prior surveys in the series, it provides data for trends. It also provides estimates for health behaviors pertaining to fitness and cardiovascular disease risk reduction, injuries and injury prevention, and sexually transmitted disease risk reduction. In addition, it offers an assessment of the mental health of military personnel, including stress and depression, and examines oral health and dental check-ups, gambling behaviors, and special gender-specific health issues pertaining to women's and men's health. REPORT DATE OCT 20032Many individuals contributed to the success of this study. Among DoD and military Services personnel, special appreciation is due to Ms. Kim Frazier, Lieutenant Colonel Michael Hartzell, Lieutenant Colonel Tom Williams, and Dr. Michael Peterson, the Cooperative Agreement Officer's Representatives, who provided valuable guidance and facilitated conduct of the study. Excellent liaison between DoD, RTI, and the Services was provided by Colonel Regina Curtis for the Army, Mr. Linden Butler and Mr. William Flannery for the Navy, Lieutenant Danisha Robbins and Mr. Cruz Martinez for the Marine Corps, and Dr. Paul DiTullio and Mr. Charlie Hamilton for the Air Force. We also gratefully acknowledge the efforts of Mr. Robert Hamilton, Ms. Carole Massey, and Ms. Sue Reinhold of the Defense Manpower Data Center for constructing the installation-level sampling frame, selecting the sample of military personnel, and relaying current military population counts used for the analysis weights. The cooperation of installation commanders, both for the pilot test and the main survey, and the assista...

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Panels of persons who volunteer to participate in Web surveys are used to make estimates for entire populations, including persons who have no access to the Internet. One method of adjusting a volunteer sample to attempt to make it representative of a larger population involves randomly selecting a reference sample from the larger population. The act of volunteering is treated as a quasi-random process where each person has some probability of volunteering. One option for computing weights for the volunteers is to combine the reference sample and Web volunteers and estimate probabilities of being a Web volunteer via propensity modeling. There are several options for using the estimated propensities to estimate population quantities. Careful analysis to justify these methods is lacking. The goals of this article are (a) to identify the assumptions and techniques of estimation that will lead to correct inference under the quasi-random approach, (b) to explore whether methods used in practice are biased, and (c) to illustrate the performance of some estimators that use estimated propensities. Two of our main findings are (a) that estimators of means based on estimates of propensity models that do not use the weights associated with the reference sample are biased even when the probability of volunteering is correctly modeled and (b) if the probability of volunteering is associated with analysis variables collected in the volunteer survey, propensity modeling does not correct bias.

Preface xi that gives more nearly complete coverage of the group but requires extensive screening to reach member of the rare group.At this writing, we have collectively been in survey research for more years than we care to count (or divulge). This field has provided interesting puzzles to solve, new perspectives on the substantive research within various studies, and an ever growing network of enthusiastic collaborators of all flavors. Regardless of how you plan to use the book, we hope that you find the material presented here to be enlightening or even empowering as your career advances. Now let the fun begin . . . . . .