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    Standard Deviation Question
    From: William Hawes
    Date: 2013 Jan 4, 17:10 -0800

    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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