Comparing oral health care utilization estimates in the United States across three nationally representative surveys

Health Services Research, April, 2002 by Mark D. Macek, Richard J. Manski, Clemencia M. Vargas, John F. Moeller

Z = ([proportion.sub.1] - [proportion.sub.2])/[[[(standard [error.sub.1]).sup.2] [(standard [error.sub.2]).sup.2]].sup.-1/2]

In comparing estimates derived from a single data instrument and survey year, we used odds ratio associations and 95 percent confidence intervals to test statistically significant differences. For efficiency, we calculated these comparisons only for the most recent version of each survey instrument.

The SAS statistical software package (SAS Institute, Inc. 1988) was used to code variables, and the SUDAAN statistical software package (Research Triangle Institutes 1995; Shah, LaVange, Barnwell,. et al. 1989) was used to yield estimates of dental visit and standard errors. We used SUDAAN because this software package takes the complex, multistage sampling design of each data source into account when it produces standard errors for confidence intervals and Z statistics.

We used full sampling weights during the analysis so that all estimates would be representative of the civilian, noninstitutionalized population of the United States. We restricted analysis to persons aged 25-59 years because all three national surveys asked persons of this age range the dental visit questions.

We also limited the analysis to this age group because it encompassed the adults that were likely to be employed and have some type of dental insurance.

RESULTS

Utilization Estimates Within Surveys and Across Survey Years

Table 1 lists the standardized proportion of adults who reported a dental visit in the previous year, according to the NHIS. The overall proportion of persons with a dental visit increased steadily from 1986 to 1993; however, only the difference in overall dental visit proportions between the 1986 NHIS and the 1993 NHIS was statistically significant (Z= -3.30, p < 0.001).

Table 2 lists the age-standardized proportion of adults that reported a dental visit in the previous year, according to NHANES I and III. The overall proportion of U.S. adults with a dental visit increased significantly from 46.9 percent during 1971-1975 to either 52.4 percent or 66.9 percent during 1988-1994, depending on whether "the last year" in NHANES III included 364 or 365 days, respectively. Note that the response categories for the NHANES I questionnaire item required that the dental visit estimate be based on a time period of less than 365 days (Figure 2). Consequently, comparisons between NHANES I and NHANES III surveys should be based on the NHANES III categorization that included only 364 days in its definition (NHANES IIIa). The differences in overall dental visit proportions between NHANES I and NHANES IIIa (Z= -3.23, p < 0.001) and between NHANES I and NHANES IIIb (Z= -12.86; p < 0.001) were each statistically significant.

Table 3 lists the age-standardized proportion of adults who reported a dental visit in the previous year, according to the three health expenditure surveys. The proportion of U.S. adults with a dental visit remained relatively stable across survey years. There were no statistically significant differences in overall proportions among the health expenditure surveys.