Using National Survey Data to Analyze Children’s Health Insurance Coverage: An Assessment of Issues. 2. Alternative Approaches to Measuring Uninsurance


The surveys discussed in the preceding section have employed somewhat different approaches to measuring uninsurance among children, and other approaches are possible. Here we discuss two dimensions of the measurement of uninsurance: (1) whether uninsurance is measured directly or as a residual and (2) the choice of reference period.

a. Measuring Uninsurance Directly or as a Residual

There is a direct approach and a more commonly used indirect approach to identifying uninsured children in household surveys. The direct approach is to ask respondents if they and their children are currently without health insurance or have been uninsured in the recent past. The alternative, indirect approach is to ask respondents if they are covered by health insurance and then identify the uninsured as those who report no health insurance of any kind. Because interest in measuring the frequency of uninsurance is coupled, ordinarily, with interest in measuring the frequency with which children (or adults) are covered by particular types of health insurance, the more common approach is the indirect one--that is, identifying the uninsured as a “residual,” or those who are left when all children who are reported to be insured are removed. This is the approach used in the CPS, the SIPP, the NHIS, and, for some of its measures, MEPS.

We are not aware of any survey that has attempted to measure uninsurance by first asking if a child is or has been without health insurance.5 However, both the CTS and the NSAF have employed a variant on the traditional approach that involves first collecting information on insurance coverage and then asking whether those people who appear to be uninsured really were without coverage or had some insurance that was not reported. For example, in the CTS, the sequence on insurance coverage ends with, “(Are you/any of you/either of you) covered by a health insurance plan that I have not mentioned?” Respondents who indicated “no” to every type of coverage were then asked:

According to the information we have, (NAME) does not have health care coverage of any kind. Does (he/she) have health insurance coverage through a plan I might have missed?

If necessary, the interviewer reviewed the eight general types of plans. The respondent could indicate coverage under any of these types of plans or could reaffirm that he or she was not covered by any plan. In the NSAF, each respondent under 65 who reported no coverage was asked,

According to the information you have provided, (NAME OF UNCOVERED FAMILY MEMBER UNDER 65) currently does not have health care coverage. Is that correct?

If the answer was yes, the question was repeated for the next uninsured person. If the answer was no, the respondent was then asked:

At this time, under which of the following plans or programs is (NAME) covered?

The sources of coverage were repeated, and the respondent was allowed to identify coverage that had been missed or to verify that there was indeed no coverage under any type of plan.

In both of these surveys, including this “verification” question converted nontrivial percentages of children from uninsured, initially, to insured. In the CTS, the responses to this question reduced the fraction of children (under 18) who were reported as uninsured from 12.7 percent to 11.7 percent (Rosenbach and Lewis 1998). In the NSAF, the verification question lowered the estimated share of children who were uninsured from about 15 percent to 11.9 percent.(6) While the uninsured are still identified as a residual, the findings from these two surveys suggest that giving respondents the opportunity to verify their status makes a difference in the proportion of children who are estimated to be without health insurance. Curiously, both the CTS and the NSAF end up with about the same proportion of children reported as uninsured. Without the verification question, however, the CTS would have estimated 2 percentage points fewer uninsured children than the NSAF. Is a verification question an equalizer across surveys, helping to compensate for differentially complete reporting of insurance coverage in the questions that precede it? Certainly that is a plausible interpretation of these findings from a survey methodological standpoint. In any event, the results from these two surveys make a strong case for including a verification question as a standard part of a battery of health insurance questions. The NHIS added such a question in 1997, although no results have been reported as yet. The Census Bureau is testing such a question in the SIPP setting. We would hope that these efforts to test the impact of a verification question would be accompanied by cognitive research that can help to explain why respondents change their responses. It would be preferable to improve the earlier questions than to rely on a verification question to change large numbers of responses.

b.Reference Periods

Estimates of the incidence or frequency of uninsurance are reported typically in one of three ways: (1) the number who were uninsured at a specific point in time, (2) the number who were ever uninsured during a year, or (3) the number who were uninsured for the entire year. Point-in-time estimates are sometimes reported not for a specific point in time, such as January 1, 1999, but for any time during a year. When described in this way, estimates should be interpreted as the average number uninsured at a point in time and not the number who were ever uninsured during the year.

Estimates of the number or percentage of children who were uninsured over different periods of time are useful for different purposes. Estimates of the number of children who were ever uninsured over a year indicate how prevalent uninsurance is. Estimates of children uninsured for an entire year demonstrate the magnitude of chronic uninsurance. Estimates of children uninsured at a point in time reflect a combination of prevalence and duration in that the more time children spend in the state of uninsurance, the more closely the number uninsured at a point in time will approach the number who were ever uninsured.

Table 2 presents estimates for all three types of reference periods, based on data from the 1992 SIPP panel. While 13.1 percent of children under 19 were uninsured in September 1993, 21.7 percent of children under 19 were ever uninsured during the year while 6.3 percent were uninsured for the entire year.

Measuring uninsurance as a residual has implications for the length of time over which children are identified as uninsured. When a survey identifies the uninsured as a residual, the duration of uninsurance that is measured is generally synonymous with the reference period. That is, children for whom no insurance coverage is reported during the reference period are, by definition, uninsured for the entire period. To identify periods of uninsurance occurring within a reference period in which there were also periods of insurance coverage, it is necessary to do one of the following: (1) ask about such periods of uninsurance directly, (2) ask whether the insurance coverage extended to the entire period, or (3) break the total reference period into multiple, shorter periods, such as months and establish whether a person was insured or uninsured in each month.7

In the March CPS, respondents are asked if they were ever covered by any of several types of insurance during the previous calendar year. Respondents can indicate that they had multiple types of coverage during the year. But because the survey instrument does not ask if respondents were ever uninsured, or how long they were covered, respondents cannot report that they were covered for part of the year and uninsured for the rest.


Period Estimate
Uninsured at a Point in Time (September 1993) 13.1%
Ever Uninsured in Year 21.7%
Uninsured Continuously throughout the Year 6.3%

In the SIPP, respondents are asked to report whether they had any of several types of insurance coverage during each of the four preceding months. The month is the reference period. To be identified as uninsured during a given month, a child must be reported as having had no coverage during the month. Thus, a child is classified as uninsured during a month only if the child was uninsured for the entire month.(8) With the SIPP data, however, we can aggregate individual months into years or even longer periods, and we can identify children who were ever uninsured during the year, where being ever uninsured means being uninsured for at least one full calendar month.

The redesigned NHIS, the CTS, and the NSAF all capture insurance status at the time of the interview--that is, literally at a point in time. Other things being equal, this approach would appear likely to yield the most error-free reports and, in addition, the least biased estimates of coverage. It also has the advantage of requiring no recall. Respondents are not asked to remember when coverage began or ended, only to indicate whether they currently have it or not.

The value of estimates for different types of reference periods depends, in part, on the accuracy with which they can be measured. If the number of children uninsured at a point in time can be measured more accurately than the number ever uninsured during a year or the number uninsured for the entire year, then there is a sense in which the point-in-time estimates are more valuable. In the next section we discuss measurement problems that affect estimates of the uninsured.