You have been asked to investigate an outbreak of gastroenteritis among patrons of a particular fast food restaurant. Because a) 45 of 65 patrons who reported eating fish there became ill, in contrast to only 5 of 350 patrons who did not eat fish; and b) samples of fish were shown to contain the microorganism believed to be responsible for the gastroenteritis, you infer that consuming the fish was a causal factor in the outbreak. The data below pertain to a second possible etiologic factor, i.e., a history of having eaten French fries (“chips”) at that restaurant.