Posted to sci.stat.consult, sci.stat.math, sci.stat.edu where the same note was separately posted -- On Thu, 27 Jul 2000 21:14:31 GMT, "Terry Chan" <[EMAIL PROTECTED]> wrote: > I have numbers (arranged in a 2x2 contingency table - smokers/nonsmokers, > respiratory disease/no disease) for our study population (of about 1,000). > I also have numbers (arranged the same way) for the general U.S. population > (from the U.S. Office of Smoking and Health). > > Is there a statistical test that allows me to compare both populations (i.e. > a test that compares the chi-square value from each population)? No, that is certainly not what you compare. "chi-squared" is a function of N (and design) so it is never appropriate to compare it unless the Ns (and design) are the same. If there is a strong association in both samples, the U.S. would have a test statistics 200,000 times larger; your first conclusion would have to be, "The U.S. sample has more than N= 1000." > > Is there a statistical test that assesses if our study population is biased > (compared to the U.S. population) and if it is biased, associates some type > of value to this bias? > > Any help will be greatly appreciated. Thanks. Q1. Does the US have more/less Smokers reported? Q2. Does the US have more/less respiratory disease reported? Those are preliminary and related questions. - keep in mind that the reporting standards are not necessarily fixed by someone's proclamation, and the reporting is not 100% accurate even when the standards are the same. Having conventional overall rates in your sample provides some encouragement that you are measuring the same thing. What you are aiming for, I think, is Q3. Is the Odds ratio for smoking and resp. disease the same in your sample? You can set this up as a log-linear model, and get the whole set of tests. I don't know what point you are trying to make, but if you claim that your ratio is DIFFERENT, the first thing you have to defend is whether your measurements are responsible. I suppose you might be proposing that you have new-and-improved criteria for "smoking" and "disease" and that is why your OR is higher. Other arguments might be tougher to make. -- 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/ =================================================================
