1. Each year the upper age limit for federally mandated coverage rises by one year, in effect.
2. Foster children may be covered by Medicaid and, depending on whose household they appear in the SIPP, could be reported as having no parents in the household.
3. The SIPP instrument includes questions on insurance coverage provided to household members by persons outside the survey household, but it is not difficult to imagine that such coverage is reported less completely than coverage provided by parents or other adults in the household.
4. The poverty thresholds, which are provided on the SIPP file, are the same thresholds that the Census Bureau used to calculate the official estimates of children in poverty in 1994.
5. Monthly poverty rates run higher than annual poverty rates, generally, but annual poverty rates obtained from the SIPP by aggregating monthly income and poverty thresholds for individuals tend to run lower than the official poverty rates estimated from the Current Population Survey (CPS). The difference in the annual estimates can be attributed in large part to the SIPP's more accurate attribution of income to family members actually present each month.
6. These estimates of Medicaid eligibility are based on a detailed simulation described in Technical Appendix A. The simulation uses monthly income (in this case for September 1994) and other characteristics--such as the child's age and family composition--measured in the same month, along with state-specific eligibility criteria. The use of monthly data yields a more accurate simulation of the actual Medicaid eligibility determination than does the use of annual data or characteristics measured only once during a year. Other things being equal, monthly income would yield more eligibles than annual income, but there are a number of factors that confound the comparison of our monthly simulation with what other researchers have done with annual data. Finally, our simulation does not include the spend down features of the medically needy program, because the SIPP does not collect medical expenditure data. Therefore we know that we understate eligibility for Medicaid. We are not aware of any other simulations that are comparable to ours in other respects but include this feature of eligibility.
7. We exclude children who were reported to be participating in Medicaid but were simulated to be ineligible. We do so because many of the simulated ineligible participants may have been eligible for Medicaid under provisions that we did not simulate. To include just the participants would be equivalent to assuming that there were no nonparticipants among this additional group of eligibles when the participation rates that we observe for children eligible under related provisions suggest that there may have been at least twice as many nonparticipants as participants.
8. If some of these children were actually enrolled in Medicaid and their coverage had simply been misreported, we would want to include them in both the numerator and denominator of the participation rate. If all of these children were actually enrolled in Medicaid, including them in this way would yield a Medicaid participation rate of nearly 83 percent.
9. It is plausible, as well, that some number of spells that lasted fewer than four months were not reported at all. On balance, we suspect that spells of 1 to 4 months in length are still overstated, but the potential exclusion of some spells altogether has implications for the estimated number of children who were uninsured at a point in time or ever in a year. In fact, all misreporting of durations may affect estimates of incidence as well..
10. Fewer than 5 percent of the uninsured children in families above 200 percent of poverty were simulated as Medicaid eligible.
11. For example, a child who was observed at age 1 in September 1993 could have turned 1 in any of the months from October 1992 through September 1993 and ended that year of age in any of the months from September 1993 through August 1994.
12. We attribute the variability that we see to sampling error.
13. Recall that the proportion eligible for all 12 months among all children is the product of the proportion eligible all 12 months among those ever eligible, which rises with age, and the proportion who are ever eligible, which declines with age.
14. The 39 percent of infants whom we find to have ever participated in Medicaid during their infancy and their average of 10.3 months of coverage imply that 33.5 percent of infants would have been covered by Medicaid at any point in time. This compares quite closely to the 34.2 percent who were reported as covered in September 1993 (Table B.3).
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