1. Five year prospective study of the incidence, clinical features, and diagnosis of achalasia in Edinburgh;Gut,1992
2. Achalasia of the esophagus in a small urban community;Mayo Clin Proc,1969
3. Achalasia. Incidence and treatment in Virginia;Va Med,1982
4. Studies of incidence and prevalence of achalasia in Nottingham area;QJM,1985
5. Achalasia in the city of Cardiff from 1926 to 1977;Digestion,1980