Table 3. Linear regression models.

		Total hip arthroplasty			Total knee arthroplasty
Independent variable ⧩		Value at WOMAC score of 50 (intercept)	Difference for 10 points of WOMAC score (slope)	Variance explained (R2)	Value at WOMAC score of 50 (intercept)	Difference for 10 points of WOMAC score (slope)	Variance explained (R2)
	Dependent variable ➢	SF12 Mental Component Score			SF12 Mental Component Score
WOMAC Pain score	Preoperative	46.9 (46.2–47.6)	2.3 (2.0–2.7)	0.14	47.8 (46.9–48.6)	2.4 (2.0–2.8)	0.13
	At 1 year	40.9 (39.7–42.1)	2.0 (1.7–2.3)	0.14	41.2 (40.3–42.2)	2.5 (2.2–2.8)	0.24
WOMAC Function score	Preoperative	46.6 (45.9–47.4)	2.2 (1.9–2.6)	0.14	46.8 (46.1–47.5)	2.4 (2.0–2.7)	0.16
	At 1 year	41.3 (40.3–42.3)	2.2 (1.9–2.5)	0.21	42.0 (41.2–42.9)	2.5 (2.2–2.8)	0.24
	Dependent variable ➢	SF12 Physical Component Score			SF12 Physical Component Score
WOMAC Pain score	Preoperative	35.8 (35.3–36.2)	2.1 (1.8–2.3)	0.24	36.7 (36.2–37.2)	1.9 (1.6–2.1)	0.19
	At 1 year	35.5 (34.4–36.5)	2.6 (2.3–2.8)	0.27	35.5 (34.8–36.3)	2.2 (2.0–2.5)	0.30
WOMAC Function score	Preoperative	35.6 (35.1–36.1)	2.1 (1.9–2.3)	0.27	35.8 (35.3–36.2)	1.8 (1.6–2.0)	0.22
	At 1 year	35.5 (34.7–36.2)	3.0 (2.8–3.3)	0.46	35.6 (35.0–36.2)	2.6 (2.4–2.8)	0.41

Stratified simple linear regression models, at both points in time, with the SF12 Physical Component Score or the SF12 Mental Component Score as dependent variables, and the WOMAC Pain or Function scores as independent variables, in patients with arthroplasty of the hip or knee. 95% confidence intervals are in parentheses. SF12: Short-Form 12-item questionnaire. WOMAC: Western Ontario and McMaster Universities Osteoarthritis Index 12-item questionnaire.