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Table 2 Estimated average incidence rate \(\left (\overline {IR}\right)\) in number of episodes per child year and estimated hazard ratios for the different covariates from model 1 i.e. \(\widehat {HR}=\text {exp} \left ({\widehat {\beta }}_{1}\right)\), and for model 2 the estimated average incidence rate, \(\left (\widehat {\overline {HR(t)}}\right)={\text {exp} {\widehat {\beta }}_{1}\ }\), as well as the estimated degrees of freedom (EDF) for the time-varying smooth function in the hazard ratio, \({\hat {f}}_{1}(t)\)

From: Flexible modelling of risk factors on the incidence of pneumonia in young children in South Africa using piece-wise exponential additive mixed modelling

 

Model 1

 

Model 2

  
 

\(\overline {IR}\) (95% CI)

\(\widehat {HR}\ \) (95% CI; p-value)

\(\overline {IR}\) (95% CI)

\(\widehat {\overline {HR(t)}}\) (95% CI; p-value)

EDF (p-value)

HU

0.29 (0.26, 0.32)

 

0.29 (0.26, 0.33)

  

HEU

0.42 (0.35, 0.51)

1.49 (1.21, 1.83; p<0.001)

0.40 (0.33, 0.48)

1.37 (1.10, 1.71; p=0.004)

1.00 (p=0.036)

Girls

0.25 (0.22, 0.29)

 

0.25 (0.22, 0.29)

  

Boys

0.38 (0.34, 0.43)

1.53 (1.28, 1.84; p<0.001)

0.37 (0.33, 0.43)

1.48 (1.22, 1.79; p<0.001)

1.00 (p=0.261)

Not low WfL

0.30 (0.26, 0.33)

 

0.29 (0.25, 0.33)

  

Low WfL

0.29 (0.25, 0.35)

0.99 (0.81, 1.22; p=0.926)

0.31 (0.26, 0.37)

1.07 (0.87, 1.33; p=0.522)

1.00 (p=0.023)

Mbekweni

0.34 (0.30, 0.38)

 

0.33 (0.29, 0.38)

  

TC Newman

0.29 (0.25, 0.33)

0.85 (0.71, 1.02; p=0.074)

0.29 (0.25, 0.34)

0.89 (0.73, 1.07; p=0.212)

1.00 (p=0.162)

Not preterm birth

0.30 (0.27, 0.33)

 

0.29 (0.26, 0.33)

  

Preterm birth

0.42 (0.34, 0.51)

1.41 (1.12, 1.77; p=0.003)

0.42 (0.34, 0.52)

1.43 (1.12, 1.81; p=0.003)

1.00 (p=0.752)

Not low birthweight

0.29 (0.26, 0.32)

 

0.29 (0.26, 0.32)

  

Low birthweight

0.46 (0.37, 0.56)

1.56 (1.23, 1.97; p<0.001)

0.47 (0.37, 0.58)

1.61 (1.26, 2.05; p<0.001)

2.11 (p=0.168)

Lower SES

0.37 (0.32, 0.41)

 

0.37 (0.33, 0.42)

  

Higher SES

0.26 (0.23, 0.30)

0.72 (0.60, 0.87; p<0.001)

0.26 (0.22, 0.30)

0.69 (0.57, 0.83; p<0.001)

1.00 (p=0.127)

Uncrowded

0.30 (0.27, 0.34)

 

0.30 (0.27, 0.34)

  

Crowded

0.34 (0.29, 0.41)

1.14 (0.94, 1.39; p=0.177)

0.35 (0.29, 0.41)

1.16 (0.95, 1.43; p=0.152)

1.01 (p=0.635)

No maternal smoking

0.28 (0.25, 0.32)

 

0.28 (0.25, 0.32)

  

Maternal smoking

0.38 (0.33, 0.45)

1.35 (1.12, 1.64; p=0.002)

0.39 (0.33, 0.45)

1.38 (1.13, 1.68; p=0.001)

1.00 (p=0.537)

Indoor air pollution unexposed

0.32 (0.28, 0.36)

 

0.32 (0.28, 0.36)

  

Indoor air pollution exposed

0.27 (0.21, 0.36)

0.85 (0.63, 1.15; p=0.279)

0.26 (0.20, 0.35)

0.83 (0.61, 1.12; p=0.224)

2.00 (p=0.337)

High maternal education

0.27 (0.23, 0.32)

 

0.28 (0.24, 0.33)

  

Low maternal education

0.34 (0.30, 0.38)

1.24 (1.03, 1.50; p=0.022)

0.33 (0.30, 0.38)

1.18 (0.97, 1.44; p=0.093)

1.47 (p=0.218)

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BMC Medical Research Methodology

ISSN: 1471-2288

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