Table 1

Design of screening studies comparing different frequencies of chest radiographic screening

Study and year commenced	Subjects	Intervention	Control	Screening duration	Total follow up*
*Follow up period includes period of active screening and post screening follow up. The maximum follow up is described; for some studies this varied as subjects were enrolled at different stages.
Erfurt County (1972)³	Men aged 40–65 years. Smokers and non-smokers	6 monthly chest radiographs	Chest radiographs every 1–2 years.	6 years	6 years
North London study (1960)¹⁴	Men aged 40+ years. Smokers and non-smokers from 119 work sites (mainly factories)	6 monthly chest radiographs	Chest radiograph at baseline and at the end of 3 years	3 years	3 years
Czech study (1976)¹⁶	Men aged 40– 64 years. Current heavy smokers.	6 monthly chest radiography and sputum cytology for the first 3 years followed by annual chest radiograph for 3 years	Chest radiograph at baseline and chest radiograph and sputum cytology after 3 years followed by annual chest radiographs for 3 years	6 years	Initially 6 years, later extended to 15 years
Mayo Lung Project (1971)⁴	Men attending the Mayo Clinic aged more than 45 years. Heavy smokers	4 monthly chest radiography and sputum cytology	Advised at the start of the study to have an annual chest radiograph and sputum cytology test	6 years	Initially 11 years, later extended to 24 years.
Kaiser Permanente study (1964)¹⁸	Men and women aged 35–54 years. Smokers and non-smokers. Members of Kaiser Permanente medical care programme	Encouraged to undergo an annual multiphasic health check up including an annual chest radiograph	Subjects not urged to undergo screening but could do so as part of their usual care if requested	16 years	16 years