In a classic study, which predates the existence of the EPO drug, Melvin Williams of Old Dominion University actually injected extra oxygen-bearing red cells into the subjects’ bloodstream just prior to a treadmill test. Twelve long-distance runners were tested in 5-mile runs on treadmills. Essentially, two running times were obtained for each athlete, once in the treatment or blood-doped condition after the injection of two pints of blood and once in the placebo control or non-blood-doped condition after the injection of a comparable amount of a harmless red saline solution. The presentation of the treatment and control conditions was counterbalanced, with half of the subjects unknowingly receiving the treatment first, then the control, and the other half receiving the conditions in reverse order.

Since the difference scores, as reported in the New York Times, on May 4, 1980, are calculated by subtracting blood-doped running times from control running times, a positive mean difference signifies that the treatment has a facilitative effect, that is, the athletes’ running times are shorter when blood doped. The 12 athletes had a mean difference running time, D, of 51.33 seconds with a standard deviation, s D, of 66.33 seconds.

a) Calculate Cohen's d for these results

b) interpret the effect size

c) How might this result be reported in literature?

d) Why is it important to counter balance the presentation of blood-doped and control the conditions?

e) Comment on the wisdom of testing each subject twice—once under the blood-doped condition and once under the control condition—during a single 24-hour period.