Children's Health Insurance Patterns: A Review of the Literature. 3. SIPP Versus CPS Estimates of the Uninsured

12/19/1997

Bennefield (1996c) compared the SIPP and CPS estimates of the uninsured and offered explanations as to why they seem to differ. Bennefield compared the CPS estimates of the uninsured for 1991, 1992, and 1993 with two types of estimates from the SIPP: (1) the SIPP first quarter average monthly estimates for 1992, 1993, and 1994, which can be considered point-in-time estimates; and (2) the SIPP estimates of those uninsured throughout the year for 1991, 1992, and 1993.

TABLE II.3
SIPP ESTIMATES OF UNINSURED CHILDREN BY SOURCE
Time Period Universe Estimate Definition Number

(Millions)

Percent Source Panel
1990 Children age 18 Average monthly uninsured 11.1 16.2% The Lewin Group (1997, Draft) not cited
Children age 17 Point-estimate of uninsured in wave 1 of 1990 panel (10/89 to 4/90) - 13.3% Urban Institute (Blumberg et al. 1997) 1990
1991 Children age 18 Average monthly uninsured 11.5 16.5% The Lewin Group (1997, Draft) not cited
1992 Children age 17 Point-estimate of uninsured in wave 8 of 1990 panel (10/89 to 4/90) - 13.3% Urban Institute (Blumberg et al. 1997) 1990
Children age 18 Average monthly uninsured 12.4 17.2% The Lewin Group (1997, Draft) not cited
1993 Children age 18 Uninsured throughout - 6.5% CBO (Bilheimer, 1997) 1992
Uninsured at any given time - 13.5%
Uninsured at least one month - 15.5%
Average monthly uninsured 13.0 17.9% The Lewin Group (1997, Draft) not cited
24-month period from February 1991 to January 1993 Children age 17 Uninsured throughout 3.0 - Families USA 1997 1991
Uninsured at least one month 20.5 -
Children age 17 uninsured at least one month Uninsured 12 months or longer 9.6 47%
32-month period from early 1991 through mid-1993 Children age 17 Uninsured throughout 2.2 3.2% Census (Bennefield 1995) 1991
Uninsured at least one month 19.6 29.0%
28-month period from early 1992 through 1994 Children age 17 Uninsured at least one month - 30% Census (Bennefield 1996b) 1992
Median number of months uninsured

TABLE II.4
SIPP ESTIMATES OF UNINSURED FOR ALL PERSONS BY SOURCE
Time Period Universe Estimate Definition Number

(Millions)

Percent Source Panel
1991 All persons Uninsured throughout - 7.0% Bennefield 1996c 1991
1992 All persons Uninsured throughout - 7.6% Bennefield 1996c not cited
Uninsured throughout 18.1 7.2% Census (Bennefield 1995) 1991
Uninsured first quarter (point-estimate) - 14.8% Bennefield 1996c not cited
Uninsured at least one month 50.7 20.3% Census (Bennefield 1995) 1991

1993

All persons Uninsured throughout 19.4 - Census (Bennefield 1996b) 1992
Uninsured throughout - 7.7% Bennefield 1996c not cited
Uninsured first quarter (point-estimate) - 14.6% Bennefield 1996c not cited
Uninsured at least one month 53.6 21.2% Census (Bennefield 1996b) 1992
1994 All persons Uninsured first quarter (point-estimate) - 14.5% Bennefield 1996c not cited
32-month period from early 1991 through mid-1993 All persons Uninsured throughout 9.7 4% Census (Bennefield 1995) 1991
Uninsured at least one month 64 26.5%
28-month period from early 1992 through 1994 All persons Uninsured throughout 11.9 4.8% Census (Bennefield 1996b) 1992
Uninsured at least one month 66.6 27.0%
Median number of months uninsured 5.7 -

He chose the SIPP first quarter average monthly estimates for his SIPP point-in-time estimates because they correspond with March, the month in which the CPS collects data about the previous year. Bennefield found that the CPS estimates are more similar to the SIPP point-in-time estimates than the annual estimates, suggesting that CPS respondents were reporting their current health insurance status ( Table II.5). He found uninsurance rates of 14 to 15 percent for all persons for both the CPS estimate and the SIPP point-in-time estimate.(15) In contrast, he found uninsurance rates of 7 to 8 percent for the SIPP annual estimates.

Bennefield showed that the estimate of the uninsured throughout a given year using the SIPP is substantially lower than CPS estimates because the SIPP has substantially more persons reporting private health insurance coverage. For example, in 1993 the SIPP showed an 81 percent annual coverage rate for private health insurance versus 70 percent for CPS; in comparison, the SIPP point-in-time coverage rate was 72 percent. Unlike estimates of private insurance, estimates of government-sponsored health insurance were generally consistent across timeframes and surveys -- the CPS Medicaid coverage rates were 11 to 12 percent for the periods analyzed, and both the annual and point-in-time SIPP coverage rates were 9 to 11 percent for the periods analyzed. It is not clear what conclusions should be drawn from the fact that private health insurance coverage accounted for much of the difference between the CPS and SIPP annual estimates. On the one hand, if recall problems were to blame for higher CPS estimates of the uninsured compared with SIPP annual estimates, then respondents seemed to be more likely to fail to recall private insurance than public insurance. Such an explanation is plausible if those publicly insured are more likely than those privately insured to have coverage throughout the year. On the other hand, CPS respondents may simply be reporting their health insurance status as of the interview date.

TABLE II.5
HEALTH INSURANCE STATUS OF ALL PERSONS: CPS VERSUS SIPP FOR VARIOUS YEARS
  1993

(or Q1 1994)

1992

(or Q1 1993)

1991

(or Q1 1992)

Percent Uninsured
CPS 15.3 14.7 14.1
SIPP Annual 7.7 7.6 7.0
SIPP Point-in-Time 14.5 14.6 14.8
Percent w/ Private Coverage
CPS 70.2 71.1 72.2
SIPP Annual 81.2 81.7 83.4
SIPP Point-in-Time 71.9 72.4 72.7
Percent w/ Medicaid
CPS 12.2 11.2 10.7
SIPP Annual 12.9 12.3 11.5
SIPP Point-in-Time 11.3 10.2 9.4
Source: Bennefield (1996c).

Even though the CPS estimates of the uninsured are more widely cited, Census Bureau officials suggest that SIPP may be better suited to measure health insurance information for a number of reasons.(16) First, the SIPP may have less recall error than the CPS because it has a shorter recall period (4 months for the SIPP versus over 1 year for the CPS). Second, respondents may be more likely to answer the SIPP health insurance questions because the questions are more detailed and are better positioned at the beginning of the interview. Third, the SIPP attempts to interview each person in the household age 15 and over, whereas the CPS interviews only one person, who may not obtain accurate information on all household members. Finally, the SIPP is especially designed to measure program participation (such as Medicaid), whereas the CPS is primarily a labor force survey.