Study group and outcome measurement
The population was composed of patients with newly diagnosed
constipation (ICD-9-CM codes=564.0) from 2000 to 2012. To ensure
accuracy of diagnoses, we excluded any diagnosis of constipation before
2000 and only patients with at least three outpatient visits or one
hospitalization were selected for inclusion in the final analysis. The
index date of this cohort was set as the first date of diagnosis of
constipation. Furthermore, to ensure that all individuals had new-onset
asthma, we ruled out any diagnosis of asthma (ICD-9-CM=493) happening
before the index date. The non-constipation group constituted subjects
who had never been diagnosed with constipation for the period 1999 to
2013.
The outcome variable was defined as a diagnosis of asthma with at least
three outpatient visits or once hospitalization. The patients were
followed up until the occurrence of atopic dermatitis, 31 December 2013,
or withdrawal from the National Health Insurance system, whichever
occurred first.