Conf. Interval: Two Indep. Means

4 Questions


Hi Professor!

A large sample confidence interval for the true average difference between quantitative GRE scores for engineering majors and physical science majors was created. The result was as follows:-45.09 < μe - μp < 95.09. Is there a significant difference? Which group had the larger sample mean?

For that specific problem, I don't know which interval is for engineering majors or physical science majors. I thought that 95.09 was for the physical science majors

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hello professor, how are we supposed to solve number 14 on the homework without that specific calculator, if n1+n2 - 2 = 52....if 52 degrees of freedom is not on our t table. Will there be any on the test like this?

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Is it safe to assume that in HW: 9.5, where The Goverment's mean is 35.50 and the Private is 54.6, that the final interval is going to be negative. (This could be in any situation) Per say if Goverment mean is 54.6 and 35.50 that the final interval is positive ?

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In the video for example 135, you state that it doesn't really matter which we take as X1 or X2 (the weight watchers or the atkins). Well, I worked out the problem with you, having done the opposite calculation (you got -.9, I got .9 because I subtracted weight watchers from atkins instead of atkins from weight watchers).

The confidence interval I got had the same numbers but different signs:

Your confident interval in the video: [-3.85,1.78]
My confidence interval: [-.178, 3.85]
I worked everything else out with you in the same manner (t alpha/2, s2p, and E).

My question is if there should be a certain way that we evaluate these problems to determine which will be x bar #1 (X1) and which will be x bar #2 (X2). I don't want to calculate any which way and get the confidence interval wrong on the exam.

Here is example 135: Among 28 subjects using the Weight Watchers diet, the mean weight loss after a year was 3.0 pounds with a standard deviation of 4.9 pounds. Among 25 subjects using the Atkins diet, the mean weight loss after one year was 2.1 pounds with a standard deviation of 4.8 pounds. Construct a 95% confidence interval estimate of the difference between the mean weight losses for the two diets (assume weight loss is a normally distributed random variable). Does there appear to be a difference between the effectiveness of the two diets? Thank you for your help!

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