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On 02 Jan 2013 [at] 16:33 Frank Reed in thread "Lunars and accuracy generally" wrote"
Greg, your first set:
"Off Arc
32.9'
32.7'
32.7'
32.4'
32.5'"
The standard deviation of that set is 0.17'.

Your second set:
"On Arc
32.4'
32.4'
32.6'
32.7'
32.7'"
The standard deviation of that set is 0.14'.

I have two Texas Instruments calculators that perform Standard Deviation calculations - a 1999 vintage TI-89 and a 2011 vintage TI-Nspire CX CAS updated to the 2012 Ver 3.2 OS. The TI-89 has a 'stdDev()' function. The TI-Nspire does not have a "plain" Standard Deviation function but rather two Standard Deviation functions; 'stdDevPop()' and 'stdDevSamp()'. The TI-Nspire 'stdDevPop()' function gives the same results as Frank calculated on the two data sets. However the TI-89 with its single 'stdDev()' function and the TI-Nspire with its 'stdDevSamp()' function give (to 3 decimal places) 0.195 and 0.152 to the above two data sets. If I hadn't updated to the TI-Nspire I would have been stuck with the TI-89 not agreeing with Frank's Standard Deviation calculation.

Not being a math wiz, when should I be using stdDevPop and when should I be using stdDevSamp? The TI-Nspire Reference Manual does not shed any light on when to use the two different Standard Deviation functions. Can anyone elaborate?

William Hawes (wmh)
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