Changes in the health insurance coverage of individuals between points in time one and two years apart give us a very good idea of the magnitudes of gross flows of children into and out of particular types of coverage over the span of one and two years. But they do not show all movement. In particular, they do not capture multiple changes by the same individuals. To gain a different perspective on changes in health insurance coverage over time, we examine changes between one month and the next. More specifically, we examine month-to-month transitions into and out of uninsurance and into and out of Medicaid.
How many children leave uninsurance each month and how many enter uninsurance each month? Tables 8 and 9 present estimates of monthly transitions out of and into uninsurance, respectively. Each of these tables is based on 23 successive cross-tabulations of insurance status between one month and the next.
For each month from October 1992 (9210) through August 1994 (9408), Table 8 reports the total number of children without health insurance, followed by a percentage distribution of their coverage in the next month, the number who became insured, and a percentage distribution of the type of insurance coverage that these latter acquired. Average monthly estimates of each of these quantities are presented at the bottom of the table, and we consider these first. On average, 9 percent of the roughly 9 million uninsured children left that state each month, with 8.3 percent becoming insured and the remainder leaving the survey universe or aging out of the child population.7 Of the 752,000 who became insured each month, 41 percent enrolled in Medicaid, 52 percent gained coverage under an employer-sponsored plan, and 7 percent obtained coverage by another type of insurance.8
The 752,000 children, on average, who became insured between one month and the next plus the additional 64,000 children who left the survey universe or turned 19 years old each month represent a sizable number. Outflows of this magnitude would have depleted the stock of uninsured children in a little over a year had there been no flows in the opposite direction. Of course, there were flows in the opposite direction, and they have to compare in magnitude to the flows out of uninsurance as the net change in the number of uninsured children over the 23 months is less than the outflow in a single month. Moreover, we know from Table 7 that 62 percent of the children who were uninsured in October 1992 were still uninsured in September 1993, and nearly 52 percent were still uninsured a year later. From the relative frequency of short durations among new spells of uninsurance, reported earlier, we can infer that most of the children who exited uninsurance during FY93 and FY94 did not become uninsured until after the start of the period. It is because of the number of children flowing into uninsurance, as we shall see below, that 9 percent of uninsured children could leave that population month after month with little effect on the total number of children who were uninsured at a point in time.
The individual monthly results that make up the bulk of Table 8 are of interest for what information they may provide on seasonal patterns and trends in exits from uninsurance. In research conducted for the Food and Nutrition Service, using the 1992 and 1993 SIPP panels, Czajka et al. (1998) found clear evidence of seasonality in the total number of children in poverty. In the research presented in Technical Appendix A, however, we found no evidence of seasonality in the total number of uninsured children. If there are any seasonal patterns in the movement of children into and out of uninsurance, of course, they would show up most clearly in the numbers of children entering and leaving uninsurance each month and in the distribution of their sources of coverage before and after spells of uninsurance.
We see no evidence of seasonality in any aspect of the monthly transitions reported in Table 8. Nor do we see clear evidence of a trend in the number becoming uninsured, even though the number without insurance declines by more than 700,000 over the 23 months. While the monthly estimates of children leaving uninsurance bounce around quite a lot, varying from a low of 564,000 to a high of 884,000, this variation appears to be due entirely to sampling error.
Table 9 reports estimates of the number of children who were without health insurance in November 1992 through September 1994, the percentage distribution of their coverage in the preceding month, the number who became uninsured in the current month, and the percentage distribution of insurance status in the preceding month among those who became uninsured. On average, 791,000 children became uninsured each month. Of this number, 52 percent had employer coverage in the preceding month, 39 percent had Medicaid coverage, about 6 percent had other coverage, and less than 3 percent were newborns or children returning to the survey universe. The distribution of prior month coverage among those becoming uninsured compares fairly closely to the distribution of prior month coverage among children who began spells of uninsurance in FY93 that lasted one to 12 months (see Table 5). As we explained above, with reference to the distribution of coverage after completion of a spell of uninsurance, this similarity of the two distributions is not at all surprising, given that Table 8 refers to all new spells that started in FY93 or FY94 (exclusive of October 1992) and Table 5 refers to a large subset of the spells that began in FY93.
In the monthly results the numbers who became uninsured in September 1993 and 1994 stand out because they are the only estimates in excess of one million. Nevertheless, there is no other evidence of seasonal change in the monthly estimates, and so we infer that there is no seasonality in the movement of children into uninsurance. Similarly, we see no seasonal swings in any of the components of change. These vary a lot from month to month but with no clear pattern, and so we conclude that their variation is due to sampling error, essentially. Nor do there appear to be any long-term trends in either the number becoming uninsured or the composition of coverage in the preceding month. The final months show a rise in the number becoming uninsured and, with it, the proportion of uninsured children who were insured the preceding month, but these are strictly short- term changes that in reality may represent nothing more than sampling error.
Table 10 shows for each month from October 1992 through August 1994 the number of children under 19 who were enrolled in Medicaid, a percentage breakdown of the types of coverage they had in the next month, the number of children leaving Medicaid in the next month, and a percentage distribution of the type of coverage that followed Medicaid. Average monthly transitions are reported at the bottom of the table. On average about 4 percent of Medicaid enrollees under 19 years of age or more than half a million children (555,000) left Medicaid each month. Of these, 56 percent became uninsured while about 37 percent acquired another form of insurance and 7 percent left the survey universe or aged out of the population of children under 19.
Table 11 reports monthly transitions into Medicaid. Of the 583,000 entering Medicaid each month, on average, just over half or 53 percent were previously uninsured, 34 percent had employer- sponsored or other insurance coverage, and 14 percent were either new to the survey universe or returning to the survey universe. In fact, virtually all if not all of those entering the survey universe were newborn children who were enrolled in Medicaid at birth (an extension of their mothers’ coverage in pregnancy, no doubt). The size of this group reflects both the high rate of Medicaid coverage among infants and the disproportionately large share of the Medicaid population that infants represent.
Neither Table 10 nor Table 11 shows any evidence of seasonality or trend in the exits from or entrances into Medicaid enrollment. That Medicaid enrollment among the SIPP population of children under 19 grows by nearly 500,000 over the period can be attributed to the fact that new enrollments tended to outnumber exits from Medicaid in each month rather than one series growing or declining more rapidly than the other.