Table 2.
Mean (standard error) for the parameters of the mixed-effects model with different combinations of covariates for model selection
| Covariates, n | Duration in seconds (CS) | Disease OA | Disease RA | Age (CS) | BMI (CS) | Seconds since getting up (CS) | Gender | Intercept | AIC |
|---|---|---|---|---|---|---|---|---|---|
| 5 | 0.50 (0.15) | 4.7 (1.19) | 0.87 (0.93) | 0.12 (0.48) | 0.02 (0.39) | 0.01 (0.07) | −1.5 (0.86) | 1.14 (0.75) | 371.32 |
| 4 | 0.55 (0.16) | − | − | 0.99 (0.57) | 0.40 (0.49) | 0.01 (0.07) | −1.46 (1.17) | 2.67 (0.61) | 383.52 |
| 4 | 0.49 (0.15) | 4.74 (1.18) | 0.89 (0.92) | 0.15 (0.47) | 0.02 (0.39) | − | −1.44 (0.85) | 1.13 (0.74) | 376.97 |
| 4 | 0.53 (0.15) | 4.68 (1.27) | 0.87 (0.99) | −0.07 (0.49) | 0.06 (0.42) | 0.01 (0.07) | − | 0.71 (0.75) | 373.77 |
| 4 | 0.50 (0.15) | 4.82 (1.07) | 0.85 (0.90) | − | 0.03 (0.38) | 0.01 (0.07) | −1.45 (0.81) | 1.10 (0.71) | 369.72 |
| 4 | 0.49 (0.15) | 4.71 (1.09) | 0.89 (0.85) | 0.13 (0.46) | − | 0.02 (0.07) | −1.50 (0.83) | 1.13 (0.69) | 369.26 |
| 3 | 0.56 (0.15) | − | − | 1.09 (0.55) | − | 0.01 (0.07) | −1.53 (1.16) | 2.69 (0.61) | 382.60 |
| 3 | 0.49 (0.15) | 4.76 (1.08) | 0.91 (0.84) | 0.15 (0.47) | − | − | −1.44 (0.82) | 1.11 (0.68) | 374.89 |
| 3 | 0.53 (0.15) | 4.73 (1.17) | 0.92 (0.90) | −0.06 (0.48) | − | 0.01 (0.07) | − | 0.68 (0.68) | 371.85 |
| 3 | 0.50 (0.15) | 4.85 (0.96) | 0.88 (0.82) | − | − | 0.02 (0.07) | −1.45 (0.79) | 1.08 (0.65) | 367.59 |
| 2 | 0.58 (0.15) | − | − | − | − | 0.01 (0.07) | −0.92 (1.20) | 2.45 (0.64) | 384.92 |
| 2 | 0.52 (0.15) | 4.67 (1.11) | 0.90 (0.95) | − | 0.05 (0.4) | − | − | 0.72 (0.71) | 377.36 |
| 2 | 0.49 (0.15) | 4.92 (0.95) | 0.91 (0.82) | − | − | − | −1.38 (0.78) | 1.05 (0.64) | 373.23 |
| 2 | 0.53 (0.15) | 4.67 (1.01) | 0.93 (0.87) | − | − | 0.01 (0.07) | − | 0.69 (0.65) | 370.19 |
| 1 | 0.59 (0.15) | − | − | − | − | 0.01 (0.07) | − | 2.19 (0.53) | 385.71 |
| 1 | 0.52 (0.15) | 4.73 (1.00) | 0.95 (0.86) | − | − | − | − | 0.68 (0.64) | 375.61 |
The values on the left of the parentheses show the regression coefficients, while the values in parentheses show the standard error. Thet value can be calculated by dividing the coefficient by the standard error. The first column shows the number of covariates (the dummy variables diseaseOA and diseaseRA are counted as one covariate). The second column shows the statistics for the regression intercept. The third column is the main independent variable, i.e., the one that varies in time and allows to predict the evolution of pain and stiffness, after centering and scaling (CS) operations (mean subtraction and division by standard deviation). The third to ninth columns show the statistics with each of the covariates. If the covariate is not present in the model, dashed lines are shown. Finally, the last column shows the Akaike information criterion (AIC). For each number of covariates, the most relevant results are shown, in terms of the AIC. RA, rheumatoid arthritis; OA, osteoarthritis.