Study group and outcome measurement
The study population was composed of patients with newly diagnosed
constipation (ICD-9-CM codes=564.0) from 2000 to 2012. To ensure
accuracy of diagnoses, only patients with outpatient visits at least
three times or one hospitalization were selected for inclusion in the
final analysis. The index date of this cohort was started as the first
date of diagnosis of constipation. Furthermore, in order to ensure that
all subjects had new-onset atopic dermatitis, we excluded any diagnosis
of atopic dermatitis (ICD-9-CM=691) occurring before the index date. The
non-constipation group constituted individuals who had never been
diagnosed with constipation (ICD-9-CM=564.0) for the period 1999 to
2013.
The outcome variable was defined as a diagnosis of atopic dermatitis
(ICD-9-CM=691) with at least three outpatient visits or once
hospitalization. The patients had been followed up until the occurrence
of atopic dermatitis, 31 December 2013, or withdrawal from the NHI
system, whichever happened first.