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

The conversion of the open-ended NHANES III utilization item to the total number of days since the last visit provided a reasonable estimate of utilization when the exact date of the dental visit was known. It required some interviewer interpretation, however, when the respondent was less sure, for example, when the survey participant reported that his or her last dental visit was "about a year ago." NHANES III dental visit data are listed in the Results and Discussion sections according to the two ways that the "past year" could have been defined.

Figure 3 lists the utilization items contained within the health expenditure surveys. The NMCES had three questions concerning dental visits. In each case, the reference period for the questionnaire items was a 3-month period between the beginning and end of each round during the 1977 survey year. The NMES combined all oral health care professionals into a single questionnaire item. The reference period for the NMES was similar to the NMCES in that respondents were asked about utilization during different 3-to 4-month time intervals over the course of the year. The MEPS posed the utilization questions in yet another way. The first of two items asked the respondent whether a dental visit was made to any type of dental professional listed on a card, and the second item asked if the respondent had seen any other type of oral health care professional listed on the card. The reference period for the MEPS was similar to the NMCES and NMES in that the questions were asked for different 3-to 4-month time periods duri ng the year. A lead statement introduced the utilization sections for each of the health expenditure surveys.

Descriptive Variables

Descriptive variables included age, gender, race/ethnicity, poverty status, and level of education. Race/ethnicity included three categories: non-Hispanic White, non-Hispanic Black, and Hispanic. In the definition of Hispanic, the NHIS and health expenditure surveys included persons from several Latin American countries and Spain, whereas the NHANES III survey included only Mexican Americans. NHANES I did not oversample Hispanics and was thus unable to provide reliable estimates for this group. Races other than White or Black were excluded from this study because of small sample sizes in each of the surveys. The poverty status variable included three categories: at or above 100 percent poverty, below 100 percent poverty, and unknown. The education variable included three categories based on number of years of formal education.

Analyses

Age is significantly associated with oral health care utilization. Because the distribution of age in the United States has changed during the past 3 decades and because the national surveys have spanned these decades, we required a way to remove the potential confounding effect of age from the derivation of dental visit estimates. In order to correct for changes in the distribution of age in the population over time and remove age as a potential confounder, we adjusted, or standardized, the utilization estimates presented in this manuscript to the age distribution of the 1990 United States population, via the direct standardization method. In the direct method of standardization, the adjusted rates are derived by applying stratum-specific rates from each of the survey populations to a single standard population, akin to adjusting for inflation in an economic evaluation. Although differences between the crude and age-standardized estimates were very small, we nonetheless included adjusted estimates in the man uscript so that changes in the distribution of age in the population could be eliminated as a possible explanation for any variations across surveys and time. We compared the proportion of the population that reported a dental visit on two levels for this investigation. For example, we based comparisons of estimates derived from two different data instruments on a two-sample t test for independent samples with unequal variance. These comparisons were calculated using a normal distribution: