... protection against secondary fibromyalgia, increased resistance to musculoskeletal micro-injury, psychologically based increase in pain threshold, innately high pain threshold influencing decision ... hospital days in the past year, and dichotomous variables for smoking, and history of arthritis, fractures, and cancer at baseline Baseline values yt = 1987 were defined as weighted means [15], yt ... Longitudinal data were analyzed using generalized estimating equations (GEE) [14] Separate analyses were conducted in which repeated measurements were coded by calendar year for questionnaire response...