[SciPy-User] from 50% probablity value to standard deviation

[josef.pktd at gmail.com]

On Tue, Jul 19, 2011 at 1:00 PM, Johannes Radinger
<johradinger at googlemail.com> wrote:
> Thank you for that answer,
> the wiki articicle helped me alot, but I've still
> some problems of understanding, probably just a
> very simple thing.
>
> My case:
>
> 50% are between -165 and +165, so my IQR=330
>
> Calculating with the factor 1.349 gives my the SD-range of
> -222.6 - +222.6 is that correct? Meaning that the SD is 222.6
>
> In the graphic of the wikipedia-articel is shown that the IQR
> is between -0.6745*SD and + 0.6745*SD...If I just try to
> solve for 165/0.6745=SD results in a SD of 244.6 ...
>
> I am not sure why, probably just a very simple mathematical problem I
> don't realise ;)
>
> Maybe you can help

std = -165 / stats.norm.ppf(0.25)

print stats.norm.cdf(165, scale=std) - stats.norm.cdf(-165, scale=std)
0.5

(checked on another computer)

Josef

>
> Thank you
> /Johannes
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