Table 2.

Adjusted Mean Perceived Stress Scale (PSS) Scores at 4 Time Points in the OPPERA Nested Case-Control Study of TMD.

		Follow-up
	Baseline Visit	Intermediate Quarter	Penultimate Quarter	Final Quarter
TMD incident cases (n = 211)
Adjusted PSS score, mean (SE)	16.3 (0.5)	16.7 (0.5)	17.3 (0.5)	17.7 (0.6)
% Change relative to baseline	Referent	2	6	9
P value for change		0.319	0.029	0.003
TMD-free controls (n = 173)
Adjusted PSS score, mean (SE)	13.6 (0.5)	14.1 (0.5)	14.4 (0.6)	14.0 (0.5)
% Change relative to baseline	Referent	4	6	3
P value for change		0.181	0.064	0.458
Contrast: cases versus controls
% Difference	20	18	20	27
P value for contrast	<0.001	<0.001	<0.001	<0.001

Adjusted means were calculated from a generalized estimating equation regression model in which the PSS score was the dependent variable; predictor variables were time of data collection (5 categories) and incident TMD case classification (2 categories) along with 2-way and 3-interactions of those predictor variables. Covariates were study site (4 categories), age (continuous measure), sex (2 categories), and race/ethnicity (5 categories). PSS scores were computed at 4 time points: the day of the baseline visit, when all subjects were TMD free; intermediate follow-up quarters were 3-mo periods after enrollment but before the penultimate quarter; the penultimate follow-up quarter was the 3-mo period preceding the final quarter; and the final follow-up quarter was the 3-mo period that coincided with the follow-up clinical visit at which incident TMD was determined. OPPERA, Orofacial Pain: Prospective Evaluation and Risk Assessment; QHU, Quarterly Health Update questionnaire; TMD, temporomandibular disorder.