Atherosclerotic risk factors and risk of myocardial infarction and venous thromboembolism; Time-fixed versus time-varying analyses. The Tromsø Study
AuthorSmåbrekke, Birgit; Balteskard Rinde, Ludvig; Hindberg, Kristian; Mathiesen Hald, Erin; Vik, Anders; Wilsgaard, Tom; Løchen, Maja-Lisa; Njølstad, Inger; Mathiesen, Ellisiv B.; Hansen, John-Bjarne; Brækkan, Sigrid Kufaas
Methods: The study included 5970 subjects enrolled in the fourth survey of the Tromsø Study (1994/95). Blood pressure, lipid levels, body mass index (BMI), diabetes and smoking status were measured at baseline, and subjects still alive at the fifth (2001/02, n = 5179) and sixth (2007/08, n = 4391) survey were re-measured. Incident events of MI (n = 714) and VTE (n = 214) were recorded until December 2010. Time-fixed and time-varying Cox regression models were used to estimate hazard ratios (HR) for MI and VTE adjusted for age and sex.
Results: Variations in BMI, blood pressure and lipid levels were small, and did not alter the risk estimates when time-varying analyses were compared to time-fixed analyses. For MI, variables that changed considerably over time yielded the greatest changes in risk estimates (HR for smoking changed from 1.80 (95% CI 1.55–2.10) to 2.08 (95% CI 1.78–2.42)). For VTE, only BMI was associated with increased risk in both time-fixed and time-varying analysis, but the risk estimates weakened in the time-varying analysis. Correction of time-fixed HRs with Rosner´s method tended to overestimate risk estimates compared to time-varying analysis.