To the Editor.
—In their description of trends for ductal carcinoma in situ (DCIS), Dr Ernster and colleagues1 provide a realistic assessment of this controversial area. However, their caution concerning the "potential risk of screening mammography in the face of questionable value of the test" for women younger than 50 years seems to demonstrate circular logic via faulty deductive reasoning.In using the deductive process, it is best to be certain that the premises in a syllogism are axiomatic, or else the conclusion will be in error. The first premise is stated in the article as "efficacy of screening mammography for women younger than 50 years has not been clearly demonstrated." Actually, an updated meta-analysis of the 7 non-Canadian trials now reveals a 24% reduction in mortality in the group aged 40 to 49 years.2 The authors would likely reply that if it takes so long to assure mortality reduction, "a