Use Welch\'s unpaired t test A professor is interested in comparing the average
ID: 3317727 • Letter: U
Question
Use Welch's unpaired t test
A professor is interested in comparing the average amount spent on textbooks for freshmen and sophomores. A random sample of 12 freshmen yielded a sample mean amount of $1036 and a sample standard deviation of $68. A random sample of 8 sophomores yielded a sample mean amount of $1227 and a sample standard deviation of $321. Construct a 90% confidence interval for the difference between the mean amount spent on textbooks by freshmen and the mean amount spent by sophomores (ie. do freshmen minus sophomores). Since the sample standard deviations are wildly different, use a method which does not assume the populations have the same variance. Assume normality.
I used the welch t test I got 7 for degrees of freedom you have to use that test I have asked this problem before and they keep using the regular t test
What is the lower confidence limit on the interval? Give your answer to two decimal places. I got 27.20 it was wrong do not know why
c) What is the upper confidence limit on the interval? Give your answer to two decimal places. I got -409.20 do not know why
I used this :
T1 - T) + t;/2 * squareroot( sºr/m) +sy/n)Explanation / Answer
The statistical software output for this problem is:
Two sample T summary confidence interval:
1 : Mean of Population 1
2 : Mean of Population 2
1 - 2 : Difference between two means
(without pooled variances)
90% confidence interval results:
Hence,
Lower confidence limit = -407.36
Upper confidence limit = 25.36
Difference Sample Diff. Std. Err. DF L. Limit U. Limit 1 - 2 -191 115.17577 7.420875 -407.36193 25.361929Related Questions
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