At 07:33 AM 9/27/01 -0700, Warren wrote:
>Now, we take our sample mean and s.d. and we compute a CI. We know >we can't say anything about a probability for this single CI...it >either >contains the mean or it doesn't. So, what DOES a CI tell us? Does it >really give you a range of values where you think the parameter is? most disciplines have various models for how they describe/explain/predict events and behaviors in each of these, there are assumptions ... i don't see how we can get around that ... one must start from SOME point of reference (of course, some models make us start from much more stringent starting points than others) to me, in statistics, particularly of the inferential type, the biggest assumption that we make that is suspect is the one of SRS ... taking random samples ... however, if we did NOT make some assumption about the data being representative of the overall population ... which SRSing helps to insure ... what can we do? what inferences could we possibly make? in the case of CIs ... no, you are not sure at all that the range you got in your CI encompasses the parameter but, what are the odds that it does NOT? generally, fairly small. (well, all bets are off if you like to build 25% CIs!) so, under these conditions, is it not reasonably assured that the parameter IS inside there someplace? this does not pinpoint WHERE within it is but, it does tend to eliminate from the long number line on which the CI rests ... what values do NOT seem to be too feasible for the parameter unfortunately, if you are interested in knowing something about some parameter and, have no way to identify each and every population element and "measure" it (of course, even then, how do you know that your measure is "pure"?)... you are necessarily left with making this inference based on the data you have ... i don't see any way out of this bind ... OTHER than trying as best possible to take a good sample ... of decent size (to reduce sampling error) ... and then trusting the results that you find if there is another way, i would certainly like to know it _________________________________________________________ dennis roberts, educational psychology, penn state university 208 cedar, AC 8148632401, mailto:[EMAIL PROTECTED] http://roberts.ed.psu.edu/users/droberts/drober~1.htm ================================================================= Instructions for joining and leaving this list and remarks about the problem of INAPPROPRIATE MESSAGES are available at http://jse.stat.ncsu.edu/ =================================================================
