For 5 of the 6 categories of outcomes identified above, the sources and therefore the completeness of the necessary data differ. For each substantive area we defined "analysis samples," i.e., that subset of the full research sample for which the data necessary for analysis were available. The analysis samples for the substantive areas were:
- Mortality--full research sample
- Hospital outcomes--6, 12, and 18 month Medicare samples
- Nursing home outcomes--6, 12, and 18 month nursing home samples
- Well-being outcomes--6, 12, and 18 month followup samples
- Receipt of formal community based services and informal care--6, 12, and 18 month in-community samples
These samples and the relationship between them are described below.
Full Sample. This sample included all of the 6,326 initially randomized individuals, and was used to estimate the impacts of channeling on mortality, as measured by whether sample members were alive at 6 and 12 months after randomization and by the number of survival days as of the end of each period. The full 18-month sample, used to estimate impacts on mortality at 18 months, included the 3,165 members of the full sample who were in the 18-month cohort. A search of state death records was conducted for all sample members not known to be alive from the interviews, and these records data were supplemented with information on deaths obtained from attempts to field followup interviews and from channeling programs' client tracking system. Sample members identified as dead from either source were assumed to be alive; hence, there was no missing data on mortality. An analysis of the validity of this assumption, presented in Wooldridge and Schore (1986, Appendix F), makes use of Medicare claims data and updated status files to verify that the assumption is correct for virtually all sample members.
The Medicare Sample. The Medicare sample was employed to examine channeling's impacts on the use of hospital and other medical services, and on home health expenditures reimbursed by Medicare. The Medicare sample is the subset of the 6,326 initially randomized individuals (the full sample) who completed baseline interviews and who were either known to be Medicare entitled or known not to be Medicare entitled. This sample was used for analyzing outcomes in the first 12 months following randomization. To be consistent with the analyses of channeling's impacts on outcome measures obtained from followup interviews, the 18-month Medicare sample was restricted to those members of the Medicare sample who were also in the 18month cohort.
The Nursing Home Samples. Because Medicare claims do not provide a complete history of nursing home use, the samples used for the nursing home analysis differed from those used for the hospital analysis. Most nursing home expenses are paid by Medicaid for Medicaid-covered individuals, and by private payment for those not covered by Medicaid. Therefore, the nursing home analysis employed a two-pronged data collection strategy, relying on Medicaid (and Medicare) records to provide complete nursing home information for sample members who were covered by Medicaid, and on provider (and Medicare) records for those who were not Medicaid-covered. However, in order to identify the relevant providers for this latter group, either a followup interview or caregiver interview had to have been completed.
These data requirements resulted in three nursing home samples, one for each six-month period. These are subsamples of the Medicare samples, and include individuals who either completed a followup interview, were Medicaid covered throughout the six-month period, or died in the period but had a caregiver who provided followup information. In addition, Medicare sample members who were dead throughout a six-month period, or who died during the period and were Medicaid-covered at the start of the period and at death were also included in the nursing home sample for that period.9
The Followup Samples. The followup samples were used to analyze outcomes obtained from the followup surveys administered at 6, 12, and 18 months after randomization. The two major categories of impact analyses which relied on these samples were those dealing with sample members' well being and functional ability and those dealing with case management services. The followup sample at 6 months included the subset of the screen sample with both a complete baseline and a complete 6-month followup interview. In like manner, the sample at 12 months was composed of screen sample members who completed a baseline and a 12-month followup (but not necessarily a 6-month interview). The 18-month sample included only those in the early cohort who completed a baseline and all three followup interviews.
The In-Community Samples. Estimation of channeling impacts on receipt of formal and informal care required data on these outcome variables from the followup surveys. The interview data on receipt of such services pertained to the reference week-the week during which the 6, 12, and 18 month interview was conducted, for sample members residing in the community at followup. Therefore, the 6, 12, and 18 month in-community samples were composed of those sample members who completed the relevant interview and were living in the community during the reference week.10
These five different sample types form a hierarchy, with each being nested, or nearly so, within the one above it. See Brown et al. (1986) for a schematic representation of the relationship between them.