Investigated lifestyle factors

To demonstrate the capabilities of our model, the following preoperative factors were included: physical activity, sports activity, smoking, body mass index (BMI) and the ability to walk long distance (1000 m). Physical activity was evaluated using the University of California Los Angeles (UCLA) activity scale [27]. In terms of UCLA, an inactive patient was one who reported no or low physical activity (categories one to three). An active patient (categories four to six) reported regular participation in mild (walking) or moderate activities, such as swimming, unlimited housework or shopping. A high degree of activity was defined as categories seven to ten, according to UCLA. Sports activity was evaluated based on the patients’ subjective estimations of their participation in sport, distinguishing between none, recreational, competitive and professional performance levels. A BMI (calculated as weight in kilograms divided by height in square metres) of 30 of over was considered obese (obesity I: BMI 30–35; obesity II: BMI > 35).

The individual factors were binarised as (i) no physical activity (UCLA categories ≤ four) versus physical activity (UCLA categories > four, performing unlimited housework and shopping), (ii) no sports activity versus sports activity (recreational, competitive and professional performance levels), (iii) smoking versus non-smoking (including ex-smokers) and (iv) normal/overweight (BMI < 30) versus obese (BMI ≥ 30).