Comparing longitudinal binary outcomes in an observational oral health study

Abstract

Observational studies continue to be recognized as viable alternatives to randomized trials when making treatment group comparisons, in spite of drawbacks due mainly to selection bias. Sample selection models have been proposed in the economics literature, and more recently in the medical literature, as a method to adjust for selection bias due to observed and unobserved confounders in observational studies. Application of these models has been limited to cross-sectional observational data and to outcomes that are continuous in nature. In this paper we extend application of these models to include longitudinal studies and binary outcomes. We apply a two-stage probit model using GEE to account for correlated longitudinal binary chewing difficulty outcomes. Chewing difficulty was measured every six months during a 24-month period between two groups of subjects: those either receiving or not receiving dental care. Dental care use was measured at six-month intervals as well. Results from our proposed model are compared to results using a standard GEE model that ignores the potential selection bias introduced by unobserved confounders. In this application, accounting for selection bias made a major difference in the substantive conclusions about the outcomes of interest. This is due in part to an adverse selection phenomenon in which those most in need of treatment (and consequently most likely to benefit from it) are actually the ones least likely to seek treatment. Our application of sample selection models to binary longitudinal observational outcome data should serve as impetus for increased utilization of this promising set of models to other health outcomes studies.

Socioeconomic inequalities in the use of dental care services in Europe: what is the role of public coverage?

“…Another limitation of the study is its cross‐sectional nature, and the fact that it is subject to reverse causality. The use of healthcare services during the previous few months cannot have an effect on the maximum education level achieved, but having used dental services reduces the onset of chewing difficulties . However, we presented socioeconomic inequality according to chewing ability, and the relationship between SEP and the use of dental services was seen in both groups.…”

Preoperative Use of Angiotensin-Converting Enzyme Inhibitors/Angiotensin Receptor Blockers Is Associated with Increased Risk for Acute Kidney Injury after Cardiovascular Surgery

“…Because this was a retrospective study, differences between patients who used ACEI/ARB and those who did not use ACEI/ARB in the outcome of interest (AKI) may be subject to bias; that is, differences in the occurrence of AKI between the two groups may reflect underlying characteristics that may also have contributed to the use of ACEI/ARB and were not measured and controlled for in our naive logistic model (15)(16)(17)(18)(19). Therefore, we also used a joint model of ACEI/ARB and AKI.…”

Racial and Socioeconomic Disparities in Health from Population‐Based Research to Practice‐Based Research: The Example of Oral Health

“…To account for this possible "selection bias," the FDCS was the first study to apply sample selection models to a longitudinal study and to binary (yes/no; e.g., onset or not) outcomes. 50 Adjustment for selection bias can make a substantial difference in conclusions made about treatment effectiveness. 50 This is due in part to an adverse selection phenomenon in which those most in need of treatment (and consequently who may be most likely to benefit from it) are actually the ones least likely to seek treatment, a phenomenon that we have come to refer to as the "paradox of dental need."…”

“…50 Adjustment for selection bias can make a substantial difference in conclusions made about treatment effectiveness. 50 This is due in part to an adverse selection phenomenon in which those most in need of treatment (and consequently who may be most likely to benefit from it) are actually the ones least likely to seek treatment, a phenomenon that we have come to refer to as the "paradox of dental need." 34 Taken to the extreme, suppose that the only persons who chose to enter the dental care system were essentially healthy individuals.…”

“…We have demonstrated using different measures of oral health and OHRQOL that adjustment for selection bias is necessary in some instances, but not in others. 23,46,50 This phenomenon may be especially salient when investigating social disparities in health because the adverse selection phenomenon can be especially strong in that context.…”