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.