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Re: [Phys-l] Basic statistics




Ludwik wrote:

What should be called a population when students measure
gravitational acceleration? Each set of five results can
be called a sample. Students try to estimate the true g in
their location. Is this their "population" ? If not then
what is the population? Why do we need the concept of
population when true values, or differences between true
values, are measured with instruments of limited precision?
Individuals can be considered as parts of instruments.

A statistician would, I believe, say that the "population" would be the
set of all _potential_ experiments done under a particular set of
conditions. If you could indefinitely repeat the same experiment, then
you would uncover the population and know its true parameters. Since we
don't have patience to repeat indefinitely (and eventually equipment or
other conditions will change), we instead perform a limited number of
experiments and treat these as a representative sample of all possible
repetitions.

This doesn't mean that more repetitions will necessarily get you closer
to the "true" value - just closer to the expected results from the
particular equipment used in a particular situation.


Tim F