The "party line" is that the chi square test will function - tell you if things are far away from expectations. However, it is also less sensitive than other tests that make some assumptions about the nature of the data. One of those assumptions might be the 'shape' of the distribution of the population.
I'm sure someone can tell you about a more sensitive test of two groups when you assume a log-Normal dist, or when you do a lambda transform of some type to achieve a more or less Normal distribution. the discussion group has already suggested a t test, whether or not you believe in a Normal population. Jay mac55 wrote: > Eric Bohlman <[EMAIL PROTECTED]> wrote in message news:<[EMAIL PROTECTED]>... > > [EMAIL PROTECTED] (mac55) wrote in > > news:[EMAIL PROTECTED]: > > > > > A simple question...... > > > > > > If you are comparing binary data from two groups with underlying > > > populations that are normal.....I assume you can use a two sample Z > > > test for binomial proportions or a chi squared test on a 2x2 > > > contingency table. > > > > > > What happens if the underlying populations aren't normal? I know > > > the Z test is out. Can you still employ the chi squared distribution. > > > If not, what non-parametric test could you use? > > > > Nothing in the logic of either test requires the assumption that the data > > be derived by dichotomizing a normal continuous variable. The Z test only > > requires that the number of cases be large enough that the normal > > approximation to the binomial is decent. > > You are correct. Let's say the data are skewed or that the > numbers aren't large enough for the normal approximation? Is Chi > squared a valid test? > > mac > . > . > ================================================================= > Instructions for joining and leaving this list, remarks about the > problem of INAPPROPRIATE MESSAGES, and archives are available at: > . http://jse.stat.ncsu.edu/ . > ================================================================= -- Jay Warner Principal Scientist Warner Consulting, Inc. 4444 North Green Bay Road Racine, WI 53404-1216 USA Ph: (262) 634-9100 FAX: (262) 681-1133 email: [EMAIL PROTECTED] web: http://www.a2q.com The A2Q Method (tm) -- What do you want to improve today? . . ================================================================= Instructions for joining and leaving this list, remarks about the problem of INAPPROPRIATE MESSAGES, and archives are available at: . http://jse.stat.ncsu.edu/ . =================================================================
