3. Say you\'re going to conduct a t procedure for the difference between the mea

Question

3. Say you're going to conduct a t procedure for the difference between the means of two populations. You decide the samples, of sizes 12 and 15, are independent. Which of the following statements are true?

I. If we pool variances, the number of degrees of freedom is 25.

II. If we don't pool variances, and we don't have access to software to compute degrees of freedom, the number of degrees of freedom is 11.

III. For a given level of confidence C, a confidence interval based on 11 degrees of freedom will be wider than one based on 25 degrees of freedom.

a. I only

b. II only

c. III only

d. I and II only

e. I, II, and III

Explanation / Answer

dof=12+15-2=25 Hence I is true

CI=x+-Z*sigma/sqrt(n) hence CI with 26 points is less wider than a CI with 12 points. Hence III is true

If we dont have software,we take the one with lesser dof.Hence II is true

Hence e)I,II and III is the answer

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