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

There are a number of reasons that the health expenditure surveys consistently yielded lower utilization estimates than the standard NHIS or NHANES. These reasons can be broadly categorized into design issues and unique approaches to assessing dental visits. For example, there were differences across surveys in terms of reference periods, lead-in statements, question wording, the way to which dental professionals were referred, and social desirability. Our discussion begins with reference periods.

On average, U.S. adults report approximately two dental visits per person per year (Bloom, Gift, and Jack 1993). When questionnaire items ask a respondent to recall such infrequently occurring events, cognitive theory suggests that the respondent is more likely to count the individual events in his or her memory than to make an estimate of the number (Blair and Burton 1987; Burton and Blair 1991; Sudman, Bradbum, and Schwartz 1996a). In addition, theory indicates that there is greater uncertainty about recalling events that occurred 90 days or more ago (Burton and Blair 1991). This uncertainty results in a greater number of events that occurred outside of a specified time period being remembered as having occurred within it than otherwise--referred to as intrusion of events (Sudman, Bradbum, and Schwartz 1996b). In addition, studies of cognitive processes indicate that respondents consistently tend to overestimate the number of events when a reference period includes a period more distant in time--referred to as telescoping (Bradbum, Huttenlocher, and Hedges 1994). There is some evidence to suggest that overestimation due to telescoping may be as high as 32 percent (Bradburn, Huttenlocher, and Hedges 1994). The three surveys incorporated a variety of reference periods. For example, the NHIS asked respondents about dental visits made during a 12-month period (Figure 1), a relatively remote interval, whereas the health expenditure surveys asked about visits made during sequential 3- to 4-month periods (Figure 3), a substantially shorter period. According to cognitive theory, a respondent to the NHIS would be more likely to include events incorrectly (intrusion) and overestimate the number of events (telescoping) than would a respondent to the health expenditure surveys, and this theoretical relationship is in keeping with our findings.

It is interesting to note that the NHANES I and NHANES III dental visit items completely lacked reference periods (Figure 2). Despite this omission, however, there was still evidence of intrusion and telescoping in these surveys. We use the explicit response categories in NHANES I and the 364-and 365-day definitions of "the past year" in NHANES III to illustrate the existence of intrusion and telescoping. The response categories for NHANES I were as follows: less than 6 months ago, 6 through 11 months ago, or 1 but less than 2 years ago. Let us assume a NHANES I respondent truly visited the dentist 13 months ago. Let us also assume that the participant could not remember exactly when the visit occurred. The respondent was asked the following: "When was the last time you visited or talked with a dentist about yourself?" He or she might have responded, "About a year ago." According to intrusion and telescoping theory, this response would have been reasonable, as the respondent would have believed (incorrectly) that his visit 13 months ago actually took place within the last year. The respondent's "about a year ago" response would subsequently have been listed under the 1 but less than 2 years ago response category by the interviewer. This response would not have been counted in a NHANES I dental visit estimate, however, as the I but less than 2 years ago category was not included among NHANES I dental visit calculations.