A researcher Investigates whether or not a new cold medication disrupts mental alertness. It is known that scores on a standardized test containing a variety of problem-solving tasks are normally distributed with u = 64 and o = 8. An random sample of n = 16 subjects are given the drug and then tested. For this sample, the mean is M = 58. Does the medicine have an effect on performance? (test this with a = .01, two-tails) Compute Cohen's d to measure the size of the treatment effect. Oa. .75 Ob. 2.00 Oc. 2.58 Od. -3.00