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- Different values for variance and std. dev in JMP vs. Excel...why?

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Jun 16, 2014 12:08 AM
(4105 views)

I'm transforming some data into ZScores. A friend transformed the data in excel and the values came up slightly different than those in JMP. When trying to track down why, I found that the variance and standard deviation in excel differed from JMP. I decided to calculate the standard deviation by hand, using excel as a glorified calculator. My variance and standard deviation still came out different than what JMP was giving me. For example, excel (mean = 1.86, var = 0.1482, st. dev. = 0.3850) and JMP (mean = 1.8533, var = 0.1512, st. dev. = 0.38889). You can see they are close, but still off. I'm not exactly sure how JMP got that mean....even with a hand-held calculator the mean is exactly 1.86. Even if I used JMP's mean to calculate the variance and standard deviation in excel, I get different numbers (using mean = 1.8533 give var = 0.1483 and st. dev. = 3.851 in excel). Note that the variance in each case is calculated as a sample variance (n-1).

Does anyone know why JMP is giving me higher values? This is important as it actually makes the difference between a P = 0.05 and P = 0.06.

Thanks for any help!

**Disregard!** I found the error. One value in my data set between excel and putting it to JMP had changed and I completely blanked on updating that value in excel. Dumb mistake!!!

Message was edited by: Jennifer Campbell-Smith

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Oh no! Disregard! I found the error! 100% my mistake and I found it in the data set.

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Jun 16, 2014 12:34 AM
(3835 views)
| Posted in reply to message from jcampbell-smith 06/16/2014 03:08 AM

These statistics should be the same in Excel and JMP. Check if any rows are excluded in the JMP data table. Excluded rows are not included in summary statistics obtained by Summary(). Also, results may differ if the Weight role is assigned to a column.

The data table in the picture below has one excluded row and one column with a Weight role.

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Nothing is excluded. Can you explain what the weight role is?

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Oh no! Disregard! I found the error! 100% my mistake and I found it in the data set.