# [SOLVED] Confidence Interval for Difference in Means

• Apr 24th 2010, 08:59 PM
lpmaxwell
[SOLVED] Confidence Interval for Difference in Means
I want to find a 95% confidence interval for difference in means of two sample groups. The mean of group 1 is 1583.467 and group 2 mean is 1017.933. S.D. is 757.0272 for group 1, and 512.5486 for group 2. Sample size for each group is 15. I came up with 483.431 confidence interval, estimating the difference at between 82.103 and 1048.965, which seems like quite a big range. Is this possible? Also, would the degrees of freedom be 14 or 28? According to my software d.g. is 28, but according to my text it would be 14. Thank you.
• Apr 27th 2010, 11:55 PM
matheagle
assuming independent samples, the df is 28
• Apr 28th 2010, 04:19 AM
lpmaxwell
Degrees of Freedom
Thank you, you confirmed the d.g. that I used.
• Apr 28th 2010, 06:51 AM
matheagle
It would be 14 if it was a paired difference experiment.
BUT given that you know the two sample st deviation which means there
is no way to compute the st deviation of the differences, this must be the two indep sample case.