Research has claimed that sleeping 10 hours a night will enhance human memory. To test this claim, a researcher selects a sample of n=25 college students. Each of the 25 students is allowed to sleep 10 hours every night in a sleep lab for 4 weeks. All of the participants are given a standardized memory test after the 4 week period. For the population, scores on the standardized memory test are normally distributed with a μ = 70 and σ = 15 . The sample of n=25 students has a sample mean of M=75.
a. Is the data sufficient to state that sleeping 10 hours had a significant effect on memory? Use a two-tailed test with an α = .05 .
b. Compute Cohen's d for this study.
The null and alternative hypothesis is ,
The test is two-tailed test.
Since , the value of the population standard deviation is known.
Therefore , use normal distribution.
The critical values are , ; From Z-table
The test statistic is ,
The test statistic is not in the rejection region.
Therefore , the test statistic leads to decision to fail to reject the null hypothesis.
Conclusion : The data does not have sufficient evidence to state that the sleeping 10 hours had a significant effect on memory.
b. The cohan's d is ,
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