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.