Re: how to compare generated values with the specified distribution basis
On 20 Sep 2001 11:05:08 -0700, [EMAIL PROTECTED] (Jon Cryer) wrote: >(quoting Robert: "even when N=20, a uniform distribution can be treated as > normal for most purposes.") > > I assume you meant to say that for N=20, the sample mean based on a random > sample from a uniform distribution can be assumed to have a normal > distribution for most purposes. > > Right? I thought he was intending the stronger statement: a lot of uniforms can be treated as normal, especially for small N and for moderate effect size. Conover, et al., showed the equivalency between doing (a) the old rank-order tests (like the MWW), and (b) simple t-tests, etc., on the rank-transformations. Robert waffles by saying 'most' purposes, so I have to find it easy to agree. When might you *not* treat a uniform, N=20 as normal? - perhaps when the R^2 is too high (above .90)? -- Rich Ulrich, [EMAIL PROTECTED] http://www.pitt.edu/~wpilib/index.html = Instructions for joining and leaving this list and remarks about the problem of INAPPROPRIATE MESSAGES are available at http://jse.stat.ncsu.edu/ =
Re: how to compare generated values with the specified distribution basis
On Thu, 20 Sep 2001 15:54:24 +0200, "JHWB" <[EMAIL PROTECTED]> wrote: > Hm, hope I didn't make that subject to complex, resulting in zero replies. > But hopefully you can answer this: > > I have a N(20,5) distribution and based on that I generated 25 values using > Minitab and the Calc>Random data>Normal function. The result yielded a mean > of 19,083 and a standard deviation of 6,0148. > > Now, how can I compare these results numerically and graphically? Compared numerically: generating parameters were mean=20, SD=5; for N=25, the observed sample has mean= 19, SD= 6, If you assume there is a known, fixed mean=20 and SD=5, then the SE for N=25 is 1; and the t-test is 1.0 A graphical comparison of 2+2 points is dull, and usually is a waste of space. Especially to illustrate "nothing interesting." There's more potential if you draw 10 or 100 samples. > I mean, in the back of my head I have an image of a graph with a straight > line (the basis for the values) and the plotted dots of the actual generated > data following the line. It is hard to describe a one-dimensional plot of 25 points, since there is hardly anything *there* that is interesting or useful. - I don't parse the description, above, on first try; I don't generate a description that sounds like that one when I do the task myself, even after several tries; so I don't know what you are describing. "Box-and-whisker" is a style that structures some information. Still, one plot is not as interesting as a dozen. -- Rich Ulrich, [EMAIL PROTECTED] http://www.pitt.edu/~wpilib/index.html = Instructions for joining and leaving this list and remarks about the problem of INAPPROPRIATE MESSAGES are available at http://jse.stat.ncsu.edu/ =
Re: how to compare generated values with the specified distribution basis
Robert: "even when N=20, a uniform distribution can be treated as >normal for most purposes." I assume you meant to say that for N=20, the sample mean based on a random sample from a uniform distribution can be assumed to have a normal distribution for most purposes. Right? Jon Cryer At 01:16 PM 9/20/01 -0300, you wrote: > > >JHWB wrote: >> >> Hm, hope I didn't make that subject to complex, resulting in zero replies. >> But hopefully you can answer this: >> >>snip > > The gotcha is that while these may be roughly equivalent questions for >(say) N=20, for N small deviations from normality are important and the >test is poor at detecting them; for N large, deviations from normality >do not matter very much but the test is hypersensitive. > > For instance: even when N=20, a uniform distribution can be treated as >normal for most purposes. However, it will generally fail the >Ryan-Joiner test at a 5% level! > > -Robert Dawson > > >= >Instructions for joining and leaving this list and remarks about >the problem of INAPPROPRIATE MESSAGES are available at > http://jse.stat.ncsu.edu/ >= > ___ --- | \ Jon Cryer, Professor Emeritus ( ) Dept. of Statistics www.stat.uiowa.edu/~jcryer \\_University and Actuarial Science office 319-335-0819 \ * \of Iowa The University of Iowa home 319-351-4639 \/Hawkeyes Iowa City, IA 52242 FAX319-335-3017 |__ ) --- V "It ain't so much the things we don't know that get us into trouble. It's the things we do know that just ain't so." --Artemus Ward = Instructions for joining and leaving this list and remarks about the problem of INAPPROPRIATE MESSAGES are available at http://jse.stat.ncsu.edu/ =
how to compare generated values with the specified distribution basis
Hm, hope I didn't make that subject to complex, resulting in zero replies. But hopefully you can answer this: I have a N(20,5) distribution and based on that I generated 25 values using Minitab and the Calc>Random data>Normal function. The result yielded a mean of 19,083 and a standard deviation of 6,0148. Now, how can I compare these results numerically and graphically? I mean, in the back of my head I have an image of a graph with a straight line (the basis for the values) and the plotted dots of the actual generated data following the line. JHWB = Instructions for joining and leaving this list and remarks about the problem of INAPPROPRIATE MESSAGES are available at http://jse.stat.ncsu.edu/ =
