Read the passage below. It summarizes survey information.
The Global Youth Tobacco Survey asks youth to fill in the answers to several questions about their tobacco use. In
this survey conducted between 2000 and 2007, it was found that in youth ages 13-15, 12 percent of boys and 7
percent of girls reported smoking cigarettes. This information was shared and reported on the American Cancer
Society website. The information was then used by several industries in the fields of health care, insurance, and
education.
What is a reason that these data may be unreliable?