Research has shown that losing even one night's sleep can have significant effect on performance of complex tasks such as problem solving (Linde & Bergstroem, 1992). To shows this phenomenon, a sample of n = 25 college students was given problem-solving task at noon on one day and again at noon on following day. The students were not permitted any sleep between two tests. For each and every student, the difference between first and second score was recorded. For this sample, the students averaged MD = 4.9 points better upon the first test with variance of s2 = 64 for difference scores.
a. Do the data point out a significant change in problem-solving capability? Employ a two-tailed test with ? = .05.
b. Calculate an estimated Cohen's d to measure the size of the effect.