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Table 1 Categorisation of the respiratory rate (RR) and PCO2 covariates from the IRYSS-COPD study, based on the proposed methodology

From: Use of generalised additive models to categorise continuous variables in clinical prediction

 

Derivation ( N = 805)

Validation ( N = 545)

Variable

Cut points

AIC

AUC

p-value*

RR

Continuous‡

 

317.10

0.634

-

RR

Dichotomised

≤ 22

318.10

0.594

0.079

  

> 22

   

RR

3-category

≤ 20

314.50

0.638

0.8198

  

(20-24]

   
  

> 24

   

RR

4-category

≤ 20

316.2

0.640

0.6833

  

(20-24]

   
  

(24-30]

   
  

> 30

   

PCO2

Continuous‡

 

250.26

0.825

-

PCO2

Dichotomised

≤ 47

281.50

0.742

≤ .0001

  

> 47

   

PCO2

3-category

≤ 43

270.76

0.779

0.0002

  

(43-52]

   
  

> 52

   

PCO2

4-category

≤ 43

258.11

0.810

0.1148

  

(43-52]

   
  

(52-65]

   
  

> 65

   
  1. Cut points were obtained in the derivation sample. AIC and AUC values were computed in the validation sample *Corresponding to the DeLong’s test for comparing the AUC of each model with the continuous option ‡AIC and AUC were calculated from the GAM
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BMC Medical Research Methodology

ISSN: 1471-2288

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