Assume that the sample is a simple random sample obtained from a normally distributed population of IQ scores of statistics professors. Use the table below to find the minimum sample size needed to be 99% confident that the sample standard deviation s is within 50%of σ. Is this sample size practical?

sigma

σ

To be 95% confident that s is within

1%

5%

10%

20%

30%

40%

50%

of the value of sigma

σ, the sample size n should be at least

19,205

768

192

48

21

12

8

To be 99% confident that s is within

1%

5%

10%

20%

30%

40%

50%

of the value of sigma

σ, the sample size n should be at least

33,218

1,336

336

85

38

22

14

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