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Hi professor,
I'm stuck on HW 9.10 on problem 4.2.
The F-Test is S1 = 128 n1 = 23 and s2=162 n2=16. Where the claim is not equal. (o1^2 not equal to o2^2). The CL = 0.02, but since its a two tail test its divided by 2 ~ x= 0.01. I ended up getting: F0.01.22.15 ~> 3.372. Your answer is 2.98. To sum this up, I'm really confused. If you could help me, thank you very much.

Posted to STATS 2 on Thursday, October 17, 2013   Replies: 2 Professor Mcguckian
10/17/2013
8:48 PM EST

Hi Andrea,

Remember that we decide which sample provides the numerator of our test statistic by determining which sample variance (or standard deviation) is bigger, so even though the problem may label one sample as sample one and the other as sample two, you cannot assume that is how they should be used in the problem to get the critical value or to form the test stat.

In this example, the second variance (162) is larger than the first group's variance (128), so we would make the second group our numerator of the test stat (basically, we treat group two as if it is our group one).  This means the degrees of freedom should be: F15, 22, 0.01.

Hope that clears it up,

Professor McGuckian .
10/17/2013
9:44 PM EST
Thanks again, helped lots.