Most readers are not aware of the fact that medical journals may have an unspoken bias in the papers that they select for publication. These biases can have far-reaching consequences. The controversy over mammography screening for women ages 40-49 is a case in point. Several medical journals knowingly have refused to provide women with accurate information. Consequently, women have been led to believe that the age of 50 has some real significance with regard to screening when the fact is that it has none.