March 2000 (Vol. 1, No. 1)
Wisconsin's Uninsured Population: How Low--4% or 11.8%
by Catherine A. Frey

Both the State of Wisconsin and the Federal Government reported their most recent estimates of the uninsured proportion in Wisconsin in the fall of 1999. The 1998 Wisconsin Family Health Survey, conducted by the Bureau of Health Information of the Wisconsin Department of Health and Family Services, estimated that 208,000 or 4% of Wisconsin household residents were without health insurance for an entire year. The US Census Bureau also collects information about health insurance coverage of U.S. residents annually through the Current Population Survey (CPS). The CPS estimated that 604,000 or 11.8% of Wisconsin household residents were uninsured for an entire year in 1998. The Family Health Survey (FHS) estimate is considerably smaller than the persons uninsured estimated by the US Census Bureau. Why are these estimates so different from each other and which one is more accurate? Both the CPS and FHS are high quality surveys, but they are conducted in very different ways and for different purposes. Major differences in measurement methods are likely to explain most of the discrepancy between estimates.

Sample Design Differences

The sample for the CPS is drawn on a national level using a national multistage cluster sample, so the data are designed to provide estimates on a national and not a state-level. Even if a large number of individuals in some states have been selected for the CPS sample, those individuals may not be representative of the state as a whole. For example, if all of the individuals sampled in a given state live in urban areas, the results would not provide a reliable description of the total population in a state with a substantial rural population. In short, the CPS can answer only nationally focused questions such as “How many people in the United States are uninsured?” The FHS conducts its survey from a representative sample of Wisconsin's population using a random sample of telephone numbers stratified by region. The sample size of the FHS is also larger than the CPS, representing a total of 6,560 Wisconsin household residents for 1998. The CPS sampled 705 households in Wisconsin from a total of 50,353 households interviewed nationally in 1998.

Differences in the Survey Purposes

The two surveys are also designed for different purposes. According to the US Census Bureau's October 1999 report, “The CPS is not designed primarily to collect health insurance data. Instead it is a largely a labor force survey, with relatively little training of interviewers on health insurance concepts.” If the interviewers are not appropriately trained to collect health insurance data, this might subtly bias the data collected. For example, many individuals may not be aware that they or their children are covered by a health insurance program, and therefore, do not report coverage. With changes in welfare reform and public assistance benefits, the Census Bureau also cautions that their results “may have resulted in a downward bias in the most recent Medicaid estimates compared with those from previous years”. The FHS in comparison is specifically designed to provide estimates of health care coverage, various health problems and use of health care services by people across the state. The FHS uses highly trained interviewers for this purpose.

Differences in Measuring Results

Probably the most important difference is in the way the uninsured are measured in the two surveys. The CPS estimates the uninsured by the “residual method”. That is, survey participants are not asked directly if they were uninsured, rather, they are assumed to be uninsured if they do not report having insurance through Medicare, Medicaid or employer-sponsored programs. So, the estimates are “residual” – the proportion that remains after those who report other means of insurance are subtracted from the total. Survey researchers believe that this method may overestimate the proportion of uninsured, unlike the FHS, which asks directly if the respondents were uninsured. Specifically, the FHS asks, “Thinking about all types of private and government health insurance, including Medicare, Medical Assistance, employer-provided coverage, and insurance that you pay for, were you covered for all 12 months since (this month last year), covered for part of that time, or not covered at all by health insurance since (this month last year)”? The CPS asks, “During the previous year, was anyone in your household covered by health insurance?” and, “Was anyone in your household uninsured yesterday?” Those individuals who report no insurance at all or who were uninsured at the time of the interview are considered to be uninsured.

Despite the differences in the estimates and the surveys, it appears that the make up of uninsured population remains consistent on a state and national level. The uninsured are more likely to be unemployed, employed part time, low-income or poor, have lower educational attainment, and are Hispanic or foreign born. CPS data over a three-year average from 1996-98, shows that Wisconsin is among the states with the lowest proportion of uninsured in the nation. The CPS reports that the proportion for Hawaii, the state with the lowest estimated proportion, is not statistically different from Wisconsin or Minnesota. While comparisons among states are useful, for planning programs for the citizens of Wisconsin, the Family Health Survey continues to be the best source of information regarding health insurance coverage among Wisconsin residents.