Table 1.

Marker Variables and Categories Used in Latent Class Modelling

		Categories and Interpretations
Marker Variable	Description of Variable (Event Type)	A	B	C	D
GP	Number of GP visits in year with ICD-9 code 493	0	1	2	≥3
OP	Number of other physician visits coded 493	0	≥1	—	—
Dx1	Number of hospitalizations in year with ICD-9 code 493 as the primary diagnosis	0	≥1	—	—
Dx2	Number of hospitalizations in year with ICD-9 code 493 as a secondary diagnosis	0	≥1	—	—
SABA	Number of short-acting beta agonist (SABA) prescription fills in year	0	1	2	≥3
ICS	Number of inhaled corticosteroid (ICS) fills in year	0	1	2	≥3
OAD	Number of other (non-SABA, non-ICS) asthma drug fills, including oral steroids, long-acting beta agonists, xanthines, leukotriene receptor antagonists, and anti-allergic agents	0	1	2	≥3

Note: Category A for a marker is assigned to patients with 0 events during a year of that particular type. Categories B, C, and D are assigned to patients with, in the case of the GP marker, 1, 2, or ≥3 GP visits for asthma (ICD-9 code 493), respectively. In the case of the OP, Dx1, and Dx2 variables—markers for relatively uncommon events—only categories A and B were assigned. The B category is used for these variables when patients had ≥1 event of their respective types.

GP, general practitioner; ICD-9, International Classification of Disease, 9th Revision.