A cognitive psychologist believes that a particular drug improves short-term memory. The drug is safe, with no side effects. An experiment is conducted in which 8 randomly selected subjects are given the drug and then given a short time to memorize a list of 10 words. The subjects are then tested for retention 15 minutes after the memorization period. The number of words correctly recalled by each subject is as follows: 9, 10, 12, 7, 10, 8, 7, 9. Over the past few years, the psychologist has collected a lot of data using this task with similar subjects. Although he has lost the original data, he remembers that the mean was 7.2 words correctly recalled and that the data were normally distributed.
(a) On the basis of these data, what can we conclude about the effect of the drug on short-term memory? Use α = 0.05_{2 tail} in making your decision.
t_{obt} = t_{crit} = ± |
(b) Determine the size of the effect.
d̂ =
From the given sample data : n=8 , ,
The samle mean is ,
The sample standard deviation is ,
a)
Hypothesis : Vs
The value of the test statistic is ,
The critical value is ,
; The Excel function is =TINV(0.05,7)
Decision : Here , the value of the test statistic lies in the rejection region.
Therefore , reject Ho.
Conclusion : Hence , we can conclude about the effect of the drug on short-term memory.
(b) The size of the effect is ,
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