What conclusions about the necessary or sufficient causes could be drawn from the following evidence? Using the concepts we have been discussing, explain why your answer is right, but also why those conclusions are not conclusive.

a. Doctors at Harvard who studied 2000 nurses for 25 years found that those who had high cholesterol came from different ethnic backgrounds, and different economic classes.

b. Studies on tadpoles found the following. If the tadpoles were spawned in pond water that averaged more than 75 degrees F, the tadpole population had a larger percentage of mutations and if the water was on average below 65 degree F there were no mutations at all. However, if the temperature varied from a high of 75 degrees F to a low of 65 degrees F then there were also no mutations.

c. Four groups of pregnant mothers were studied. The first group was given a shake that was high in protein but low in iron every breakfast. The second group was given a shake low in protein but high in iron. The third group was given a shake high in both protein and iron. The final group was given a shake that contained no iron or protein. After three weeks, the women in the third group had more stable blood sugar throughout the day than the women in other three groups.

d. Partners at a local marketing firm did a study at 20 local shoe stores. The firm found the following: stores that played music with a slow beat had the worst sales of all the stores, even worse than those that played no music at all. Those that played music with a fast beat had the best sales, and among those, the ones that played it loudest had the best sales. The researchers found no other commonalities among the different groups of stores.