Re: Random Sampling and External Validity
Here is how I resolve that problem: Define the population from the sample, rather than vice versa -- that is, my results can be generalized to any population for which my sample could be reasonably considered to be a random sample. Maybe we could call this "transcendental sampling" ;-) -- it is somewhat like transcendental realism, defining reality from our percetion of it, eh? - Original Message - From: "dennis roberts" <[EMAIL PROTECTED]> To: "Elliot Cramer" <[EMAIL PROTECTED]>; <[EMAIL PROTECTED]> Sent: Thursday, March 22, 2001 7:54 AM Subject: Re: Most Common Mistake In Statistical Inference > > > here is my entry for the most common mistake made in statistical inference ... > > using and interpreting inference procedures under the assumption of SRS > simple random samples ... when they just can't be > > this permeates across almost every technique ... and invades almost every > study ever published ... > > if not in an internal validity sense ... surely in an external validity sense = Instructions for joining and leaving this list and remarks about the problem of INAPPROPRIATE MESSAGES are available at http://jse.stat.ncsu.edu/ =
Re: Random Sampling and External Validity
At 12:56 PM 3/25/01 -0500, Karl L. Wuensch wrote: >Here is how I resolve that problem: Define the population from the sample, >rather than vice versa -- that is, my results can be generalized to any >population for which my sample could be reasonably considered to be a random >sample. Maybe we could call this "transcendental sampling" ;-) -- it is >somewhat like transcendental realism, defining reality from our percetion of >it, eh? this sounds like the method of grounded theory in the qualitative bailiwick ... look at data you have and see what you can make of it that is ... there is no particular PLAN to the investigation ... data gathering ... or, what you want to do with what you find after the fact i try to tell students this is not a very good strategy ... = Instructions for joining and leaving this list and remarks about the problem of INAPPROPRIATE MESSAGES are available at http://jse.stat.ncsu.edu/ =
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Re: 1 tail 2 tail mumbo jumbo
On Mon, 19 Mar 2001 13:14:39 -0500, Bruce Weaver <[EMAIL PROTECTED]> wrote: > On Fri, 16 Mar 2001, Rich Ulrich wrote: [ snip, including earlier post ] > > That ANOVA is inherently a 2-sided test. So is the traditional 2x2 > > contingency table. That is because, sides refer to hypotheses. > > > > > I agree with you Rich, except that I don't find "2-sided" all that > appropriate for describing ANOVA. For an ANOVA with more than 2 groups, > there are MULTIPLE patterns of means that invalidate the null hypothesis, > not just 2. With only 3 groups,for example: > > A < B < C > A < C < B > B < A < C [ ... ] > And then if you included all of the cases where 2 of the means are equal > to each other, but not equal to the 3rd mean, there are several more > possibilities. And these ways of departing from 3 equal means do not > correspond to tails in some distribution. > > There's my attempt to add to the confusion. ;-) If I convince people that they want only one *contrast* for their ANOVA, then it is just two-sided. I've been talking people out of blindly testing multiple-groups and multiple periods, for years. Then I have to start over on the folks, to convince them about MANOVA. If there are two groups and two variables, there are FOUR sides -- and that's if you just count what is 'significant' by the single variables. Most of the possible results are not useful ones; that is, they are not easily interpretable, when no variable is 'significant' by itself, or when logical directions seem to conflict. We can interpret "group A is better than B." And we analyze measures that have the scaled meaning, where one end is better. So the sensible analysis uses a defined contrast, the 'composite score'; and then you don't have to use the MANOVA packages, and you have the improved power of testing just one or two sides. -- 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/ =
