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Table 1 Distribution of predictor values and outcome, and predictor effects in multivariable logistic regression models

From: Prediction models for clustered data: comparison of a random intercept and standard regression model

  Distribution (N = 1642) Interquartile range per anesthesiologist * Standard model Beta (95% CI) † Random intercept model Beta (95% CI) †
Fixed effect     
Female gender 882 (54%) 46%-63% 0.75 (0.53 – 0.97) 0.78 (0.54 – 1.01)
Age, years ‡ 49 (16.5) 46-51 -0.008 (-0.014 – -0.001) -0.009 (-0.016 – -0.003)
History of PONV or motion sickness 530 (32%) 30%-36% 0.41 (0.19 – 0.64) 0.42 (0.18 – 0.65)
Current smoking 510 (31%) 20%-33% -0.43 (-0.66 – -0.19) -0.45 (-0.69 – -0.20)
Abdominal or middle ear surgery 209 (13%) 4%-16% 0.62 (0.32 – 0.93) 0.57 (0.24 – 0.89)
Volatile anesthetics 844 (51%) 33%-74% -0.03 (-0.24 – 0.18) 0.19 (-0.09 – 0.46)
Intercept 616 (38%) § 29%-47% § -0.65 (-1.05 – -0.25) -0.68 (-1.16 – -0.19)
Random effect     
Intercept variance †† - - - 0.15 (0.07 – 0.33)
  1. * interquartile ranges of the predictor distributions per anesthesiologist.
  2. † logistic regression coefficients with 95 percent confidence intervals. Intervals of the random intercept model were based on the t-distribution.
  3. ‡ mean (standard deviation).
  4. § number (percentage) of patients with PONV, rather than the intercept is reported.
  5. PONV = post operative nausea and vomiting.
  6. †† non-parametric confidence interval of the random intercept variance was obtained from a cluster bootstrap procedure.