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Re: [Phys-l] sample variance versus population variance



"... whether you should buy cat food or dog food.
It all depends. If you have a cat, buy cat food. If you have a
dog, buy dog food."

Not exactly; dogs will thrive on cat food but not the reverse. Insufficient protein density in the dog fud.

bc



John Denker wrote:

On 10/09/2006 07:21 PM, Krishna Chowdary wrote:


Thanks for your response, John. I don't think that's the question I was
asking. I tried to ask my question more explicitly in the rest of the
message you refer to, and tried to define my notation. Please let me know
what I might need to clarify or restate.

My question is not about sample variance vs. population variance. In a
nutshell, it is about whether the standard deviation or the standard
deviation of the mean (of a data set consisting of time measurements) should
be used when propogating uncertainty through a calculation.


Well, I still think that the "nutshell" question is isomorphic to the
sample_variance versus population_variance question. Rereading the
previous message tells me the same thing.

At some very abstract level, asking whether you should propagate the
standard deviation (i.e. sqrt of population variance) or propagate
the standard deviation of the mean (i.e. sqrt of sample variance)
is sorta like asking whether you should buy cat food or dog food.
It all depends. If you have a cat, buy cat food. If you have a
dog, buy dog food.

At the not-so-abstract level, I'm pretty sure that for present
purposes you want to model the population, not the sample. You


cut