Table 4 Excluded studies in which oesophageal pH monitoring was performed in patients with asthma, and the reasons for exclusion

Reference	Sample size <50	Population source not reported	Patients referred for suspected GORD	pH Monitoring for <24 hours	ATS criteria for asthma diagnosis not satisfied	Prevalence of abnormal oesophageal acid exposure in patients with asthma (%)
Perrin-Fayolle et al 198037					✓	138/150 (92.0)
Perpina et al 198350	✓	✓		✓		9/26 (34.6)
Ducolone et al 198751	✓	✓		✓		11/21 (52.4)
Ekstrom and Tibbling 198852	✓		✓			18/37 (48.6)
Nagel et al 198853	✓				✓	15/44 (34.1)
Guidicelli et al 199054					✓	76/121 (62.8)
DeMeester et al 199055					✓	54/77 (70.1)
Larrain et al 199156				✓	✓	94/142 (66.2)
Herve et al 199357		✓				41/53 (77.4)
Gastal et al 199458	✓		✓			12/25 (48.0)
Schnatz et al 199659			✓		✓	42/54 (77.8)
Suh et al 199760	✓				✓	11/42 (26.2)
Campo et al 199761	✓		✓			14/17 (82.4)
Dal Negro et al 199962	✓					30/37 (81.1)
Harding et al 199939			✓			128/199 (64.3)
Garcia-Compean et al 200063					✓	34/57 (59.6)
Harding et al 200041	✓		✓			16/26 (61.5)
Heaney et al 200343					✓	31/54 (57.4)
Oldigs 200464			✓		✓	39/63 (61.9)
Paleev et al 200565	✓				✓	17/37 (45.9)
Hsu et al 200566		✓	✓			29/56 (51.8)
Sami et al 200667			✓		✓	25/50 (50.0)
Wong et al 200668	✓					17/30 (56.7)