A corporate liability trial. A major court case on the health effects of drinking contaminated water took place in the town of Woburn, Massachusetts. A town well in Woburn was contaminated by industrial chemicals. During the period that residents drank water from this well, there were 16 birth defects among 414 births.
In years when the contaminated well was shut off and water was supplied from other wells, there were 3 birth defects among 228 births.
The plaintiffs suing the firm responsible for the contamination claimed that these data show that the rate of birth defects was higher when the contaminated well was in use.
How statistically significant is the evidence? What assumptions does your analysis require? Do these assumptions seem reasonable in this case?