Fig. 1

Bootstrap frequency of covariates selection in the final model using stepwise algorithms. Dependent variable is EuroQoL 5D visual analogue scale measure of the health-related quality of life. a shows results of backward elimination regression using AIC, b—using BIC, and c—using Likelihood Ratio Test (p = 0.05). d, e and f show results of forward selection regression with AIC, BIC and LRT (p = 0.05) correspondingly. Black bars represent variables selected in the final model, and light grey bars—variables excluded from the final model. Solid line and the number next to it correspond to the minimum frequency among variables included in the final model; dashed line and the number next to it correspond to the maximum frequency among variables excluded from final subset. Dotted line corresponds to the frequency = 0.9, and number next to it shows the percentage of variables in the final model with inclusion frequency over 0.9 (out of the number of variables selected in the final model). Description of variable names is provided in the Additional file 2