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    Re: Standard Deviation Question
    From: Greg Rudzinski
    Date: 2013 Jan 4, 21:00 -0800

    Here are 20 index error observations of Procyon using a Tamaya Jupiter with 7 x 35mm scope.

    0.2' 0.7'
    0.4' 0.7'
    0.4' 0.6'
    0.6' 0.4'
    0.8' 0.6'
    0.6' 0.7'
    0.7' 0.7'
    0.7' 0.4'
    0.7' 0.7'
    0.5' 0.4'
    n=20
    _
    x = 0.575'
    Sx = 0.1585'

    All observations are off the arc.

    Greg Rudzinski

    [NavList] Re: Standard Deviation Question
    From: Bill Morris
    Date: 4 Jan 2013 19:30
    "...when should I be using stdDevPop and when should I be using stdDevSamp?"

    Not being a maths whiz either (nor a statistician)I would say that for small numbers you should use stdDecSamp. As a rule of thumb, I have always regarded a sample of less than 30 as being "small". As you have seen, using the stdDevPop function gives you a larger figure for the standard deviation.

    The difference is unimportant in large samples. For example in 60 estimations of index error , the SD pop was 0.228 and the SD sample was 0.226.

    I am inlcined to doubt the value of giving SDs for samples of n = 5. A sample size of n = 10 seems to be marginal; 20 would be more better. May we have a statistician's ruling?

    Bill Morris
    Pukenui
    New Zealand


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