Covariates and matching
The baseline characteristics were age, gender, hypertension
(ICD-9-CM=401-405), chronic liver disease (ICD-9-CM=571), hyperlipidemia
(ICD-9-CM=272.0-272.4), diabetes (ICD-9-CM=250), chronic kidney disease
(ICD-9-CM=585), chronic obstructive pulmonary disease (COPD) (ICD-9-CM
=491, 492, 496), cardiovascular disease (ICD-9-CM=410-414), stroke
(ICD-9-CM=430-438), cancer (ICD-9-CM=140-208), and autoimmune disease
(ICD-9-CM=710.0, 720.0, 714.0). The comorbidities were defined as
occurring within one year prior to the index date with outpatient visits
at least three times or once hospitalization. In addition,
corticosteroids and antihistamines during the study period were
contained and defined as usage for at least ≧30 days.
Then, propensity score matching based on age, gender, hypertension,
hyperlipidemia, chronic liver disease, chronic kidney disease, diabetes,
COPD, cancer, cardiovascular disease, stroke, autoimmune disease,
corticosteroids, and antihistamines was performed in order to balance
the heterogeneity of the two groups. The propensity score was considered
a probability that was estimated through logistic regression. The binary
variable was the constipation group and non-constipation group.