amount of time schizophrenics

In Problem 21 of Chapter 12, a student conducted an experiment on 25 schizophrenic patients to test the effect of a new technique on the amount of time schizophrenics need to stay institutionalized. The results showed that under the new treatment, the 25 schizophrenic patients stayed a mean duration of 78 weeks, with a standard deviation of 20 weeks. Previously collected data on a large number of schizophrenic patients showed a normal distribution of scores, with a mean of 85 weeks and a standard deviation of 15 weeks. These data were evaluated using ?? = 0.052 tail. The results showed a significant effect. For the present problem, assume that the standard deviation of the population is unknown. Again, using ?? = 0.052 tail, what do you conclude about the new technique? Explain the difference in conclusion between Problem 21 and this one.