PMT statistics issue

Poisson statistics, right?

John

yup

If you are counting random events, the standard deviation on your count is just the square root of the accumulated count. Successive counts are likely to differ by around a standard devaition. A range of +/-2 standard deviations includes about 95% of a long series of counts,

+/-2.5 standard deviations gets this up to about 99%.

--
Bill Sloman, Nijmegen

If I sampled the erect status of my c*ck at one sample per day for forty-five days what is the probability that it is permanently floopy?

DNA

100% ?:-)

...Jim Thompson

--
|  James E.Thompson, P.E.                           |    mens     |
|  Analog Innovations, Inc.                         |     et      |
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I love to cook with wine.      Sometimes I even put it in the food.

"Jim Thompson" wrote in message news: snipped-for-privacy@4ax.com...

Bugger!

DNA

What about conecutive 45 sample means?

So that's why its floopy? You need to find new friends, or lay off the female hormones.

--
Service to my country? Been there, Done that, and I\'ve got my DD214 to
prove it.
Member of DAV #85.

Michael A. Terrell
Central Florida

I would hope 100% if your talkin to me. LOL

Try bottom posting.

If each sample covers the same amount of time on the same source, the standard deviation of the mean over the 45 samples has a standard deviation that is root 45, or 6.71 smaller than the standard deviation on any single mean.

There are a couple of ways of screwing this up, but you will have to read up on elementary statistics before you start needing to worry about the tricky stuff.

--
Bill Sloman, Nijmegen

I'm not sure I understand what you're saying.

Heres the question in a simplified manner.

If I measure the counts acquired in 1 second, 45 consecutive times, and calculated an average of those 45 samples and came out with say a mean of

700 counts / sec.

Standard Dev. would be sqrt(700) = ~26 assuming a poisson distribution

If I ran this test say 10 times. How much scatter in the MEAN would I expect for the consecutive runs of the 45 sample test?

I realize that the next 1 second sample would fall with in 3 sigma of the mean but I'm curious about how to calculate standard deviation of the means of several 45 sample tests.

If your mean count rate is 700counts/sec, the standard deviation on a single 1 second observation is 26.5 counts.

If you accumulate 45 seconds worth of 700count/sec data, you've got

45x700 counts -31,500 counts, and the standard deviation on that is going to be 177.5.

This implies that you then know that your count rate is 700+/-10 counts per second with 99% confidence.

If you process is stable at 700 counts per second., the standard deviation on any one second sample will stay at 26.5 counts, and any 45 second sample will have a standard deviation of 177.5 counts.

Note that if you got a count of 700 after one second of observation, all you can say about the "true"count rate is that is has an even chance of lying between 673.5 and 726.5, and that 99 times out of a hundred it will lie between 633.75 and 766.25.

As you average over long time periods, the confidence limits on the mean count rate creeps down, but the standard deviation on a single one second measurement isn't going to change at all (unless you were unlucky with your first few measurements).

--
Bill Sloman, Nijmegen

Now that is crystal clear.

Thanks.