ALCOHOL-CONTAINING MOUTHWASHES AND OROPHARYNGEAL CANCER - A SPURIOUS ASSOCIATION DUE TO UNDERASCERTAINMENT OF CONFOUNDERS

Recently it has been suggested that the use of alcohol-containing mout hwashes may increase the risk of oropharyngeal cancer. Heavy alcohol i ntake and tobacco use are established causes of oropharyngeal cancer. Their use is associated with mouthwash use. In addition, alcohol and t obacco use both tend to be underreported. Here the authors show that, under the hypothesis that mouthwash does not increase the risk of orop haryngeal cancer, confounding due to underascertained exposure to alco hol and tobacco would result in a spuriously elevated odds ratio for m outhwash use. As a general principle, a null association becomes appar ently positive if a confounding variable is incompletely ascertained: a spurious association may be produced even in the absence of a differ ence in the extent of the underascertainment of the confounder among t he comparison groups.