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Re: Why multiply t by sample std dev?
Posted:
Oct 2, 2012 9:38 AM


On 01/10/2012 9:54 PM, Rich Ulrich wrote: > On Mon, 1 Oct 2012 12:45:45 0700 (PDT), Paul > <paul.domaskis@gmail.com> wrote: > >> On Sun, 30 Sep 2012 12:55:11 0700 (PDT), Paul >> <paul.domas...@gmail.com> wrote: > > ... snip a bunch > >> Thanks, Dave, Rich, >> >> I think I pinpointed the source of my confusion. I didn't really >> know what t was. It was just a curve and a table that we blindly used >> according to a recipe. Well, Wikipedia > (http://en.wikipedia.org/wiki/Student%27s_tdistribution) defined the > tvalue in a manner similar to >> Rich: >> >> [ (sample mean)  (population mean) ] / (sample standard deviation) >> > > No! > It does not say that. It uses the sample standard ERROR. > You are going to confuse yourself on into the future if you do > not grasp the distinction and keep it clear. > > The Standard Error is the name used for the SD of a statistic. > Yes, it is also a standard deviation. But the "SD of a sample" > is distinct and larger than the "SD of a sample mean."
And to complete the thought, the (estimated) standard error (SE) of the MEAN = the sample SD divided by the square root of the sample size.
 Bruce Weaver bweaver@lakeheadu.ca http://sites.google.com/a/lakeheadu.ca/bweaver/Home "When all else fails, RTFM."



