Chemicals in butter-flavoring: Workers in a microwave popcorn production plant in Missouri breathe chemicals that are part of the butter-flavoring. Are these workers at greater risk of developing lung problems? To investigate this question, 135 workers at the plant receive a survey, and 117 respond.

Researchers want to compare workers in the popcorn production area with workers who have jobs in other parts of the plant. People in these other jobs are not directly exposed to the butter flavorings. Of the 97 workers in the production area, 30 reported experiences of “shortness of breath.” Of the 20 workers in other jobs, only 1 reported “shortness of breath.”

What can we conclude from this study? Check all that apply.