A Study Was Conducted on Horses to Identify Factors That

Multiple Choice

A study was conducted on horses to identify factors that might contribute to the formation of enteroliths-stones that form in the colon of the horse and eventually lead to blockage and death. The table below summarizes disease status, cases that have enteroliths by whether a horse has been altered (geldings have been castrated, mares and stallions have not been altered) and by whether the horse gets the majority of its feed as alfalfa. In the above table, when we look at the conditional probabilities of being a case, given being altered or not, we find that among those not fed alfalfa, horses that are not altered have a probability of being a case 3.3 times that of geldings. We find a similar ratio for the probabilities of horses fed alfalfa. When we calculate the ratio of those probabilities, combining the two tables when data are broken down by alfalfa feeding status, we find the probability of being a case, given a horse is not altered, is 6.4 times that of an altered horse. This is an example of:

A) a lurking variable.
B) Simpson's paradox.
C) Options (a) and (b) are correct.
D) None of the answer options is correct.