Covariates and matching
The baseline characteristics were age, gender, hypertension
(ICD-9-CM=401-405), hyperlipidemia (ICD-9-CM=272.0-272.4), chronic
kidney disease (ICD-9-CM=585), chronic liver disease (ICD-9-CM=571),
chronic obstructive pulmonary disease (COPD) (ICD-9-CM =491, 492, 496),
cancer (ICD-9-CM=140-208), diabetes (ICD-9-CM=250), cardiovascular
disease (ICD-9-CM=410-414), stroke (ICD-9-CM=430-438), 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 at least three
outpatient visits or once hospitalization. Besides, corticosteroids and
antihistamines during the study period were included and defined as
usage for at least ≧30 days. To assess the severity of constipation, we
collected additional information on the total numbers of laxatives
prescription (anatomical therapeutic chemical [ATC] classification
system code A06A), which occurred within one year after the index date.
Moreover, propensity score matching based on age, gender, hypertension,
hyperlipidemia, chronic kidney disease, chronic liver disease, COPD,
cancer, diabetes, cardiovascular disease, stroke, autoimmune disease,
corticosteroids, and antihistamines was applied to balance the
heterogeneity of the two groups. The propensity score was a probability
that was estimated through logistic regression. The binary variable was
the constipation and non-constipation group.