Table 2 The associations of the percentage change in BMI with outcomes of knee and hip osteoarthritis, when percentage change in BMI is either treated as a categorical variable (in the categorical analysis, left), or as a continuous variable (in the continuous analysis, right)
From: Researchers in rheumatology should avoid categorization of continuous predictor variables
Outcomes | Categorical analysis (The percentage change in BMI is treated as a categorical variable) | Continuous analysis (The percentage change in BMI is treated as a continuous variable) | ||
|---|---|---|---|---|
5% or more decrease in BMIa | 5% or more increase in BMIa | 5% decrease in BMI | 5% increase in BMI | |
Odds ratio (95% confidence interval) P-value | ||||
Knee | ||||
 Knee structure | ||||
  Progression in overall structural defects | 0.68 (0.51 0.91) 0.010 | 0.95 (0.76 1.20) 0.680 | 0.93 (0.87 0.99) 0.025 | 1.02 (0.98 1.06) 0.300 |
  Progression in medial or lateral JSN | 0.58 (0.42 0.81) 0.001 | 1.01 (0.79 1.28) 0.958 | 0.90 (0.83 0.98) 0.011 | 1.11 (1.02 1.20) 0.011 |
  Progression in medial JSN | 0.53 (0.35 0.79) 0.002 | 1.10 (0.84 1.45) 0.497 | 0.86 (0.78 0.95) 0.002 | 1.16 (1.06 1.28) 0.002 |
  Progression in lateral JSN | 0.74 (0.43 1.27) 0.268 | 0.79 (0.49 1.26) 0.314 | 1.01 (0.87 1.16) 0.907 | 0.99 (0.86 1.14) 0.907 |
  Progression in medial tibia osteophytes | 0.89 (0.67 1.18) 0.415 | 1.19 (0.94 1.51) 0.143 | 0.94 (0.87 1.02) 0.115 | 1.06 (0.98 1.15) 0.115 |
  Progression in lateral tibia osteophytes | 1.02 (0.73 1.43) 0.887 | 0.96 (0.71 1.30) 0.792 | 1.04 (0.95 1.15) 0.415 | 0.96 (0.87 1.06) 0.415 |
  Progression in medial femoral osteophytes | 0.66 (0.49 0.91) 0.010 | 1.22 (0.96 1.55) 0.098 | 0.85 (0.79 0.93)  < 0.001 | 1.17 (1.08 1.27)  < 0.001 |
  Progression in lateral femoral osteophytes | 0.97 (0.69 1.37) 0.880 | 0.97 (0.72 1.30) 0.821 | 0.98 (0.89 1.08) 0.672 | 1.02 (0.93 1.12) 0.672 |
  Incidence of total knee replacement | 0.94 (0.53 1.64) 0.818 | 1.15 (0.57 2.35) 0.692 | 0.99 (0.85 1.16) 0.916 | 1.01 (0.86 1.18) 0.916 |
 Pain in knee | ||||
  Development of frequent pain | 0.98 (0.76 1.26) 0.848 | 1.41 (1.15 1.73) 0.001 | 0.90 (0.84 0.96) 0.003 | 1.11 (1.04 1.19) 0.003 |
  Development of any pain | 0.89 (0.68 1.16) 0.383 | 1.11 (0.88 1.40) 0.365 | 0.92 (0.85 0.99) 0.020 | 1.09 (1.01 1.17) 0.020 |
  Resolution of frequent pain | 1.31 (1.04 1.64) 0.021 | 0.93 (0.75 1.14) 0.485 | 1.11 (1.04 1.18) 0.003 | 0.90 (0.85 0.97) 0.003 |
  Resolution of any pain | 1.41 (1.10 1.82) 0.007 | 1.00 (0.80 1.27) 0.968 | 1.10 (1.02 1.18) 0.011 | 0.91 (0.85 0.98) 0.011 |
Hip | ||||
 Hip structure | ||||
  Progression in overall structural defects | 0.94 (0.60 1.48) 0.798 | 1.21 (0.84 1.75) 0.306 | 0.96 (0.85 1.08) 0.527 | 1.04 (0.92 1.17) 0.527 |
  Progression in medial or lateral JSN | 1.20 (0.84 1.72) 0.318 | 1.18 (0.85 1.65) 0.324 | 0.95 (0.85 1.06) 0.343 | 1.06 (0.94 1.18) 0.343 |
  Progression in medial JSN | 1.28 (0.84 1.93) 0.248 | 1.15 (0.77 1.71) 0.495 | 0.96 (0.84 1.10) 0.549 | 1.04 (0.91 1.19) 0.549 |
  Progression in lateral JSN | 1.03 (0.61 1.74) 0.902 | 1.17 (0.74 1.85) 0.502 | 0.98 (0.84 1.16) 0.852 | 1.02 (0.87 1.19) 0.852 |
  Progression in superior acetabular osteophytes | 1.80 (0.97 3.34) 0.062 | 1.62 (0.91 2.89) 0.099 | 1.09 (0.89 1.34) 0.392 | 0.91 (0.74 1.12) 0.392 |
  Progression in inferior acetabular osteophytes progression ~  | 2.70 (1.14 6.41) 0.024 | 1.75 (0.71 4.32) 0.225 | 1.18 (0.86 1.62) 0.307 | 0.85 (0.62 1.16) 0.307 |
  Progression in superior femoral osteophytes | 1.05 (0.64 1.74) 0.841 | 1.05 (0.66 1.67) 0.826 | 1.04 (0.89 1.21) 0.658 | 0.97 (0.83 1.13) 0.658 |
  Progression in inferior femoral osteophytes | 0.74 (0.30 1.81) 0.512 | 0.78 (0.34 1.83) 0.574 | 0.99 (0.77 1.28) 0.950 | 1.01 (0.78 1.30) 0.950 |
  Incidence of total hip replacement | 1.15 (0.57 2.35) 0.692 | 1.09 (0.55 2.17) 0.806 | 1.01 (0.82 1.24) 0.947 | 0.99 (0.81 1.22) 0.947 |
 Pain in hip | ||||
  Development of frequent pain | 0.95 (0.71 1.28) 0.754 | 1.11 (0.88 1.41) 0.387 | 0.95 (0.87 1.02) 0.160 | 1.06 (0.98 1.15) 0.160 |
  Development of any pain | 0.86 (0.67 1.10) 0.227 | 0.94 (0.77 1.16) 0.582 | 0.99 (0.93 1.06) 0.779 | 1.01 (0.94 1.08) 0.779 |
  Resolution of frequent pain | 1.06 (0.79 1.42) 0.698 | 0.87 (0.67 1.14) 0.314 | 1.03 (0.95 1.12) 0.457 | 0.97 (0.89 1.05) 0.457 |
  Resolution of any pain | 1.05 (0.83 1.33) 0.697 | 1.14 (0.93 1.40) 0.201 | 0.98 (0.92 1.05) 0.541 | 1.02 (0.96 1.09) 0.541 |