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Professor,
I need help with question 18 from section 9.4. Could you please show how you get the test stat of 11.44, I get something different.
Thank You.

Posted to STATS 2 on Wednesday, October 9, 2013   Replies: 3

Professor Mcguckian
10/09/2013
1:06 PM EST

Hi Peggy,

I can create a video for this later, but for now, let me just explain here:

Because we assume equal variances for this problem, we first need to calculate Sp²

Sp² = [(n1-1)*S1² + (n2-1)*S2²]/(n1 + n2 - 2)

(27*4.51² + 28*3.98²)/(28+29-2) = 18.04934364 = Sp²

Then our test stat formula for this problem would be:

t = (Xbar1 - Xbar2) / SqrRoot(Sp²/n1 + Sp²/n2) = (38.28 - 25.4) / SqrRoot(18.04934/28 + 18.04934/29) = 11.443

Note: the denominator part of the test stat (the part under the squareroot) should be 1.125615643. Use that to check your calculation.

Hope that helps,

Professor

Professor Mcguckian
10/09/2013
7:17 PM EST

Hi Peggy,

Here is a video explanation of how to work out the test statistic:

.
10/09/2013
9:05 PM EST
Thank you Professor. I see what I was doing wrong now.