Colorectal cancer is the second most common cause of death from cancer in Europe and the United States.1 2 Population screening trials using the guaiac faecal occult blood test have reduced mortality by around 16%.3 National or regional colorectal cancer screening programmes and pilot studies for the general population have recently been introduced in more than 50 countries.4 Such organised screening programmes are the best way to reduce the incidence of colorectal cancer.

In the linked study (doi:10.1136/bmj.a2261), Malila and colleagues report the test, episode, and programme sensitivities for a new randomised method of introducing population screening for colorectal cancer in 2004 in Finland.5 Test sensitivity refers to the proportion of colorectal cancer cases detected by the test in the preclinical phase of the disease. Episode sensitivity is a function of test sensitivity (confirmed by diagnostic testing) that incorporates interval cancers not detected during the time between screening tests. Programme sensitivity is a much broader concept and is based on the proportion of total cancers detected for all people invited to participate in screening (that is, those who do and do …