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Table 3 Cox regression multivariable prediction model for patients with negative FOBTs only n = 187,470, 735 events

From: The use of electronic healthcare records for colorectal cancer screening referral decisions and risk prediction model development

Variable

Hazard Ratio

Observed Coefficient

Bootstrapped Standard Error

z

P > z

[95% Confidence Intervals]

Smoking Status

 Ex-smoker (reference category non-smoker)

1.238

0.214

0.078

2.75

0.006

0.061

0.366

 Current smoker (reference category non-smoker)

1.499

0.405

0.148

2.74

0.006

0.116

0.694

Sex Female (reference category male)

0.777

−0.252

0.074

−3.42

0.001

−0.397

−0.108

(Age/10)− 2*

−

− 1581.596

639.251

−2.47

0.013

− 2834.505

− 328.687

(Age/10)− 2x ln(Age/10) *

−

1094.918

460.929

2.38

0.018

191.514

1998.322

Previous Negative BCSP FOBTs *

0.761

−0.272

0.066

−4.11

<0.001

−0.403

− 0.142

GP ordered Blood Test

1.286

0.251

0.067

3.76

<0.001

0.121

0.382

IBS Diagnosis

1.415

0.347

0.123

2.83

0.005

0.106

0.588

  1. Abbreviations: CI = confidence intervals, FOBT = faecal occult blood test (specifically guaiac). The continuous variables (Age/10)−2has been centred at 0.023, (Age/10)− 2x ln(Age/10) at 0.043, Previous negative BCSP FOBTs at 0.510. A ‘*’ indicates that the variable is treated as continuous
  2. Survival Probability
  3. \( S(2)={0.9909}^{\exp \left(0.21{x}_1+0.41{x}_2-0.25{x}_3-1582\left(\ {\left(\frac{x_4}{10}\right)}^{-2}-0.023\right)+1095\left(\ {\left(\frac{x_4}{10}\right)}^{-2}\ast \ln \left(\frac{x_4}{10}\right)-0.043\right)-0.27\left({x}_5-0.510\right)+0.251{x}_6+0.347{x}_7\right)} \)
  4. 0.9909  baseline CRC free survival at 2 years S0(2) (the re-estimated shrunken baseline CRC free survival at 2 years was also 0.9909 when rounded) the heuristic shrinkage factor was 0.914 where S(2) is the survival probability at 2 years (probability of not being diagnosed with colorectal cancer/polyps)
  5. Event Probability
  6. P = 1 – S(2).
  7. Where P is the probability of colorectal cancer/polyp being diagnosed within 2 years of the latest FOBT date; x1ex-smoker; x2current smoker; x3sex; x4age at FOBT; x5Previous negative BCSP FOBT; x6GP ordered blood test; x7presence of IBS.
  8. There were 735 events (sample population = 187,470) and considered 16 degrees of freedom giving 45.94 events. The final model had 8 degrees of freedom with an AIC of 16,686.66 and BIC of 16,723.46 (N = 735 when calculating BIC)). Overall model fit was assessed using adjusted R2which was 0.066 (bootstrapped CI 100 reps: 0.046, 0.100). Regular R2was 0.072 (95% CI: 0.047, 0.102) with D statistic of 0.572. The linear predictor from this model had a mean of − 0.021 and a standard deviation of 0.363 (range: -1.418 to 1.206, IQR: -0.287 to 0.211).
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BMC Gastroenterology

ISSN: 1471-230X

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