@MASTERSTHESIS\{IMM2011-06089,
    author       = "K. Ranc",
    title        = "Statistical analysis of association between long-term exposure to air pollution and repeated hospitalizations for pneumonia",
    year         = "2011",
    school       = "Technical University of Denmark, {DTU} Informatics, {E-}mail: reception@imm.dtu.dk",
    address      = "Asmussens Alle, Building 305, {DK-}2800 Kgs. Lyngby, Denmark",
    type         = "",
    note         = "Supervised by Professor Per Bruun Brockhoff, pbb@imm.dtu.dk, {DTU} Informatics, and Zorana Jovanovic Andersen",
    url          = "http://www.imm.dtu.dk/English.aspx",
    abstract     = "This thesis deals with statistical methods and their application on the association between longterm exposure to traffic-related air pollution (for up to 39 years) in Copenhagen and hospital admissions for pneumonia, in a prospective cohort study. The purpose of this study is to investigate whether the exposure to air pollution is a risk factor for pneumonia hospitalizations, as well as it is associated with recurrent admissions.
The Danish Cancer Society provided data on 57053 participants of Danish Cancer, Diet and Health cohort, aged 50-65 years at baseline (1993-1997), which were followed in Danish hospital discharge register for all hospital admissions for pneumonia up to 2010. Traffic pollutants considered are nitrogen dioxide (NO2) and nitrogen oxides (NOx), available as mean annual levels estimated at residential addresses since 1971. We modelled the association between mean NO2 and NOx levels and hospitalizations for pneumonia using the Cox regression, in the full cohort and separately for people with and without previous hospital admissions for pneumonia and with and without co-morbidities defined by Charlson index.
In order to explore the association between the exposure to air pollution and the first or recurrent pneumonia hospitalizations this thesis contains a variety of statistical survival methods both standard and extended. The applied models are the ordinary Cox model, Andersen-Gill model, Conditional Andersen-Gill model, Frailty model, and Conditional Frailty model. The model are first introduced and then applied.
The investigation showed that during 12.7 years’ mean follow-up, 3024 (5.7\%) out of 53239 eligible people were admitted to hospital for pneumonia, and among those individuals 626 (1.2\%) had more than one pneumonia admission. Mean NO2 levels were significantly positively associated with risk for first pneumonia hospitalization in the full cohort (hazard ratio and 95\% confidence interval per double mean exposure: 1.25; 1.14-1.36); in 46462 people without earlier hospitalizations for pneumonia or co-morbid conditions defined by Charlson (1.23; 1.11- 1.36), and in 6292 people with history of co-morbid conditions defined by Charlson (1.22; 1.02- 1.46).
The highest risk was observed in 485 people with a history of pneumonia hospitalizations (1.68; 1.01-2.81) which led to the idea of investigating the effect of exposure to air pollution on recurrent pneumonia hospitalizations. Conditional Frailty model revealed that mean NO2 levels were also significantly positively associated with risk for recurrent pneumonia hospitalization in full cohort, up to 3 admissions per subject (1.30; 1.19-1.41).
From these findings we concluded that living in areas with high traffic-related air pollution increases the risk of hospitalization for pneumonia. The effect was highest in people with prior hospitalizations for pneumonia."
}