Re: Variance question

In article <ef27c50.-1@xxxxxxxxxxxxxxxx>, "Robin R"
<deleterobin@xxxxxxxxx> wrote:

Hello,
I have poisson data of unknown mean. Want to calculate the variance.
1) Should I take the mean
2)or do square of standard deviation (x-mu)^2 approach

what is the difference between the two??

which one I should use

Robin
-------------------
If all you want is the sample variance, then all you need to write is
the single matlab statement:

v = cov(x);

where x is the vector of your sample. You should bear in mind, however,
that the 'cov' function itself has had to find the sample's mean in order
to do its calculation. There is no need to work by way of the standard
deviation unless that is what you want to find. (Note: the 'cov' function
is so named because it is also capable of finding the covariance of a
multiplicity of variables involving a matrix of sample values.)

(Remove "xyzzy" and ".invalid" to send me email.)
Roger Stafford
.

Relevant Pages

  • Re: Standard Deviation
    ... differences from the mean is there, but the main information is in the most significant digits, rather than being computed as the difference between two very large numbers, i.e. in the least significant digits. ... standard deviation to prove your point, but the opposite can easily be ... squared deviations from the mean) OR the variance (the SS divided by N ... point was simply that with the "wrong kind of data" the square of SumX ...
    (borland.public.delphi.non-technical)
  • Re: Variance and moment
    ... the usual way of getting a standard deviation is first get the variance and then take its square root. ... Prev by Date: ...
    (sci.math)
  • Re: A Gambling Math Question
    ... The standard deviation is approximately sqrt. ... comes from the well-known normal approximation to the binomial ... The variance, which is the square of the standard deviation, can be ...
    (sci.math)
  • Re: Beginner question about sqrt()
    ... I am trying to calculate the standard deviation with my program, ... Those numbers for n> 1 and each x real are both always positive, and the corresponding standard deviations are the positive square roots of those variances. ... Neither the variance nor the standard deviations are ever negative. ...
    (comp.lang.c)
  • Re: Whenever you see a post by Luis A. Afonso, read THIS first
    ... the concept of the variance of a sample of data as ... then cut into chips. ... It has an average and it has a standard deviation. ... Reef Fish wrote: ...
    (sci.stat.math)