2.5. Statistical analysis
The participants in the control cohort group were identified using 1:4
matching in which the nearest available person for each case was
selected as a matched cohor14. We compared the
baseline characteristics (age, sex, type of insurance, Charlson
Comorbidity Index)15 using the McNemar test because
each asthmatic patient was matched to several non-asthmatic patients.
The Kaplan-Meier method was used to estimate survival curves during the
follow-up period, and survival was compared among groups using the
log-rank test. Hazard ratio (HRs) with 95% confidence interval (CI) for
the mortality of patients in the asthma cohort compared with subjects in
the control cohort were evaluated using an age- and sex-stratified Cox
regression model. To evaluate the effects of asthma-related pulmonary
comorbidity (e.g., COPD, bronchiectasis, pneumonia, lung cancer, and NTM
infection) on mortality in patients with asthma compared with subjects
without asthma, the asthma cohort was classified into two groups based
on comorbidity. Next, we performed age- and sex-adjusted Cox regression
to evaluate the effects of respiratory comorbidity on HR for mortality
in asthmatic patients compared with subjects without asthma. All
analyses were conducted using SAS 9.4 (SAS Institute, Cary, NC, USA).
All tests were two-sided, and p-values <0.05 were considered
statistically significant.