Table 1.

Candidate predictors to be assessed for inclusion in models (adapted from Blakey et al⁵)

Variable	Description
Sex	Male or female
Age	In years at the start of the 3-year study period
BMI	Last recorded, in kg/m2; categorised as underweight (<18.5), normal (18.5–24.9), overweight (25- 29.9) or obese (≥30)
Ethnicity	Ethnicity information if available (white, black, Asian, South Asian Caribbean etc)
Smoking status	Last recorded, categorised as never smoker, current smoker or ex-smoker
Charlson comorbidity index	Score in the baseline year, categorised as 0, 1–4, 5–9, ≥10
Comorbidities*	Recorded ever or active: eczema, allergic and non-allergic rhinitis, nasal polyps, anaphylaxis diagnosis, anxiety/depression diagnosis, diabetes (type 1 or 2), GERD, cardiovascular disease, ischaemic heart disease, heart failure, psoriasis
Comedications	In baseline year, prescription (yes/no) for paracetamol, NSAIDs, beta-blockers, statins
% predicted PEF	Recorded ever, expressed as percentage of predicted normal, categorised as unknown,<60%, 61%–79% and ≥80%
Blood eosinophil count	Last recorded, in 109 cell/L, categorised as ≤0.4 or >0.4
BTS step†
Step 1	Inhaled SABA as needed
Step 2	ICS or LTRA
Step 3	Add LABA to ICS or use high-dose ICS (≥400 mg/day FP equivalent)
Step 4	Add LTRA/Theo to (ICS+LABA) or add LABA/LTRA/Theo to high-dose ICS
Step 5	Add OCS
Average daily dose of SABA/ICS	Cumulative dose of SABA/ICS prescribed in baseline year, expressed in mg/day albuterol or FP equivalent and divided by 365.25
Prescribed daily ICS dose	Dose of ICS prescribed at last prescription of baseline year in mg/day, FP equivalents
ICS medication possession ratio	ICS refill rate during the baseline year: sum of number of days per pack (number of actuations per pack/number of actuations per day)/365.25
ICS device type	In baseline year: categorised as no ICS, MDI, BAI or DPI
Spacer use with ICS pMDI	Recorded in baseline year (yes/no)
Oral corticosteroid use	Any maintenance prescription for corticosteroids in baseline year (yes/no)
Prior asthma education	Recorded ever (yes/no)
Primary care consults	Number of primary care consultations, categorised as 0, 1–5, 6–12, ≥13
Primary care consults for asthma	Number of primary care consultations with an asthma-related Read code
Antibiotics with lower respiratory consult	Number of consultations that resulted in antibiotic prescription (included to capture asthma events that may have been misclassified as LRTI)
Acute respiratory events	Number of events in the baseline year, defined as asthma-related hospitalisation or ED attendance or an acute course of OCS or antibiotics prescription with lower respiratory consultation
Acute OCS courses	Number of acute courses of OCS in baseline year, categorised as 0, 1, ≥2
Acute OCS courses with lower respiratory consult	Number of OCS courses with Read code for lower respiratory consultation in baseline year, categorised as 0, 1, ≥2
Antibiotics courses	Number of antibiotics prescriptions with Read code for lower respiratory consultation in baseline year, categorised as 0, 1, ≥2
Hospital attendance/admission	Number of asthma-related‡ ED, inpatient and outpatient attendance/admission in baseline year (as recorded in primary care data)
Asthma attacks	Number of asthma-related‡ hospital ED attendance, inpatient admission or acute OCS course
Eosinophil count	Blood eosinophil count (cells/L) categorised into high and not high (threshold of 0.35×109 cells/L) to define high/not high eosinophil count24

*Comorbidity recorded ‘ever’ was defined as a diagnostic Read code during the baseline year or at any time before baseline. ‘Active’ refers to those for which a diagnosis was recorded within the baseline year and/or a previous diagnosis was accompanied by a prescription for the comorbidity within the baseline year. ‘Rhinitis’ included allergic and non-allergic rhinitis.

†Based on the British guideline on the management of asthma (October 2014) for adults and children.²⁵

‡Any patient with a lower respiratory Read code (asthma or LRTI code).

BAI, Breath-actuated inhaler; BMI, body mass index; BTS, British Thoracic Society; DPI, dry powder inhaler; ED, emergency department; FP, fluticasone propionate; GERD, gastro-oesophageal reflux disease; ICS, inhaled corticosteroids; LABA, long-acting beta antagonists; LRTI, lower respiratory tract infection; LTRA, leukotriene receptor antagonist; MDI, metered-dose inhaler; NSAIDs, non-steroidal anti-inflammatory drugs; OCS, oral corticosteroids; PEF, peak expiratory flow; SABA, short-acting b2 agonist; Theo, theophylline.