Table 3 Included studies in which 24 hour oesophageal pH monitoring in patients with asthma was performed

Reference	Country	Study design	Patient recruitment	Population source	Prevalence of abnormal oesophageal acid exposure in patients with asthma (%)
Sontag et al 199030	USA	Cross-sectional	Consecutive	Secondary care, asthma clinic	85∗/104 (81.8)
Suzuki et al 199725	Japan	Cross-sectional	Not reported	Secondary care	42/58 (72.4)
Vincent et al 199726	France	Cross-sectional	Consecutive	Secondary care, asthma clinic	30/94 (31.9)
Kiljander et al 199949	Finland	Cross-sectional	Not reported	Secondary care, asthma clinic	57/107 (53.3)
Carmona-Sanchez et al 199928	Mexico	Cross-sectional	Consecutive	Secondary care, asthma clinic	45/60 (75.0)
Compte et al 200034	Spain	Cross-sectional	Consecutive	Secondary care, asthma clinic	12/81 (14.8)
Al-Asoom et al 200323	Saudi Arabia	Cross-sectional	Consecutive	Secondary care, asthma clinic	22/50 (44.0)
Kiljander and Laitinen 200435	Finland	Cross-sectional	Random sample of consecutive patients	Secondary care	32/90 (35.6)
Leggett et al 200524	UK	Cross-sectional	Not reported	Secondary care, asthma clinic	29/52 (55.8)