After stinging its victim, the honeybee leaves behind the barbed stinger, poison sac, and muscles that continue to pump venom into the wound. A study compared two methods of removing the stinger left behind: scraping off with a credit card or pinching off with thumb and index finger. A total of 40 stings were induced on volunteers. Twenty were removed with the credit card method, and twenty were removed with the pinching method. The size of the welt left by each sting was measured ten minutes later. All 40 measurements came from two volunteers, every of whom received one treatment ten times on one arm and the other treatment ten times on the other arm.
a. The data were analyzed using a two-sample t-test with a sample size of 20 for each treatment. What is wrong with this approach? verify the problem by name, and describe how it can lead to misleading results.
b. What test would be a better choice for these data?
c. Suggest an improvement in the experimental design.