Was it the orange juice?

When there is an episode of food poisoning affecting many people, careful recording of data and the application of statistical methods are often required to identify the source.

An example was the epidemic of food poisoning on domestic airline flights in Australia in August 1991. It was suggested that the orange juice was the problem. But was it? And how could you be sure? Suppose that nearly all of those who drank the orange juice got sick, and most of those did not drink it, stayed well. Does that prove it? What do you think?

The answer is no that evidence alone is insufficient. Importantly, the people who drank the orange juice may have also eaten the bread. You need to sort out all the foods and drinks consumed by passengers before you have a clear picture. To look at orange juice in particular, you need to ask the question: among people whose consumption of other food and drinks was identical, did the OJ drinkers get sicker than the non-OJ drinkers?

We need to consider another aspect of the evidence: if it was the orange juice, why didn't everyone who drank it get sick? We need to find out about the possible means of infection. Here good detective work depends on both the statistician and another expert.