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Suppose that I want to construct a confidence interval for a two-sample problem with degrees of...

  1. Suppose that I want to construct a confidence interval for a two-sample problem with degrees of freedom k = 35. Using the t.dist function in Excel, tell me what confidence level C we would get if we used a t* of 1.690. Explain how you get from the t.dist function to your final answer here.

Aside: Notice that it is the same basic formula as all our other confidence intervals:

CI = our estimated mean ± a critical value * a standard deviation

And, by the way, remember that we call the standard deviation by the name “standard error” when we had to estimate it from the data.

  1. (0.25 pts) How large a sample should I have before I can reasonably justify using t procedures even for clearly skewed distributions?
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Answer #1

Level of Significance ,    α =    0.1
Degree of freedom, DF=   n1+n2-2 =    35
t-critical value =    t α/2 =    1.690   (excel formula =t.inv(α/2,df)
.................

Both samples >=30, so normal approximation holds            
.....................


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