The use of "no evidence" statements in public health

Public health communication makes extensive use of a linguistic formulation that will be called the "no evidence" statement. This is a written or spoken statement of the form "There is no evidence that P" where P stands for a proposition that typically describes a human health risk. Danger lurks in these expressions for the hearer or reader who is not logically perspicacious, as arguments that use them are only warranted under certain conditions. The extent to which members of the public are able to determine what those conditions are will be considered by examining data obtained from 879 subjects. The role of "no evidence" statements as cognitive heuristics in public health reasoning is considered.