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MathGroup Archive 2000

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Re: continuously updating mean confidence interval (MeanCI)

  • To: mathgroup at smc.vnet.net
  • Subject: [mg24620] Re: continuously updating mean confidence interval (MeanCI)
  • From: John Doty <jpd at w-d.org>
  • Date: Fri, 28 Jul 2000 17:23:58 -0400 (EDT)
  • References: <8lj9bq$8th@smc.vnet.net>
  • Sender: owner-wri-mathgroup at wolfram.com

Daniel Reeves wrote:
> 
> Suppose you're running a long simulation to generate a bunch of data
> points, and you want to compute the mean.  You can do this by just storing
> the cumulative sum and the count as you generate the data.
> 
> If you also want a 95% confidence interval on the mean, what is the
> minimum amount of state you need to store?
> 
> I think this reduces to finding the Variance, and I fear that the answer
> is "the whole history of data points"

No reason to fear. The sample variance is the the mean of the squares
minus the square of the mean, so the only extra thing you need is the
sum of the squares of your data points, for which you need not keep the
history.

-- 
John Doty		"You can't confuse me, that's my job."
Home: jpd at w-d.org
Work: jpd at space.mit.edu


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