Study methods, recruitment, sociodemographic findings, and demographic representativeness in the OPPERA study

Abstract

This paper describes methods used in the project "Orofacial Pain Prospective Evaluation and Risk Assessment" (OPPERA) and evaluates sociodemographic characteristics associated with temporomandibular disorders (TMD) in the OPPERA case-control study. Representativeness was investigated by comparing sociodemographic profiles of OPPERA participants with population census profiles of counties near study sites and by comparing age and gender associations with TMD in OPPERA and the 2007 to 2009 US National Health Interview Survey. Volunteers aged 18 to 44 years were recruited at 4 US study sites: 3,263 people without TMD were enrolled into the prospective cohort study; 1,633 of them were selected as controls for the baseline case-control study. Cases were 185 volunteers with examiner-classified TMD. Distributions of some demographic characteristics among OPPERA participants differed from census profiles, although there was less difference in socioeconomic profiles. Odds of TMD was associated with greater age in this 18 to 44 year range; females had 3 times the odds of TMD as males; and relative to non-Hispanic-Whites, other racial groups had one-fifth the odds of TMD. Age and gender associations with chronic TMD were strikingly similar to associations observed in the US population. Assessments of representativeness in this demographically diverse group of community volunteers suggest that OPPERA case-control findings have good internal validity.

Perspective: Demographic associations with TMD were consistent with population benchmarks and with other studies, suggesting broad applicability of these OPPERA findings. Greater occurrence of TMD in non-Hispanic-Whites than in other racial/ethnic groups and the lack of a socioeconomic gradient contradicts the disparities seen in many other health conditions.

Figure 1. Components of the OPPERA study

Once every three months, a Quarterly Health Update (QHU) questionnaire is administered. It includes questions that screen for presence of TMD-like symptoms.

1. ①

   The prospective cohort study enrolled 3,263 people who had no history of TMD symptoms and who were found not to have TMD when examined clinically. During follow-up, those people who respond positively to QHU screening questions about TMD symptoms are invited to an OPPERA study site for clinical examination to determine TMD case-classification.

2. ②

   For the baseline case-control study, 185 people with chronic TMD were enrolled as examiner-classified cases and their data were compared with baseline data from a randomly-selected half of people in the prospective cohort study.

3. ③

   For each incident case in the inception cohort, one person who screens negatively for TMD symptoms is selected as a matched control and that person is also clinically examined. People classified without TMD are included in the matched case-control study of incident TMD.

4. ④

   Follow-up of first-onset cases of TMD and their matched controls is conducted through Quarterly Health Update questionnaires. Six months after case-classification, people with first-onset TMD are invited to an OPPERA study site for another clinical examination that classifies presence or absence of TMD.

Figure 2. TMD prevalence in the US population and proportion of cases in the OPPERA baseline case-control study

A: Prevalence of self-reported TMD-like pain in the US population from the 2007-09 National Health Interview Survey (NHIS; n=72,836 people). Cases were people who responded positively to the interview question: “During the past three months have you had facial ache or pain in the jaw muscles or the joint in front of the ear?” B: Site-adjusted proportion of cases in the OPPERA case-control study (n=185 TMD cases and 1,633 controls). Proportions are predicted probabilities computed from a logistic regression model with predictor-variables age-group, gender, and age-group by gender interaction. Because the number of cases was determined by study design, the proportions are not estimates of population prevalence. However, the demographic patterns of variation in proportions seen in the OPPERA case-control study comparable to demographic patterns of variation in prevalence within the US population.