Timothy, I believe you are mistaken. Fisher's exact test give the correct answer even in the face of small expected values for the cell counts. Pearson's Chi-square approximates Fisher's exact test and can give the wrong answer when expected cell counts are low. Chi-square was developed because it is computationally "simple". Fisher's exact test, particularly with tables larger than 2 by 2 can be computationally complex. The value of the Chi-square statistic becomes closer and closer to Fisher's exact test as the expected cell counts become larger. John John Sorkin M.D., Ph.D. Chief, Biostatistics and Informatics Baltimore VA Medical Center GRECC and University of Maryland School of Medicine Claude Pepper OAIC University of Maryland School of Medicine Division of Gerontology Baltimore VA Medical Center 10 North Greene Street GRECC (BT/18/GR) Baltimore, MD 21201-1524 410-605-7119 - NOTE NEW EMAIL ADDRESS: jsorkin@grecc.umaryland.edu >>> Timothy Mak 9/12/2005 11:45:28 AM >>> I have heard that people favour the Pearson's Chi-square over Fisher's exact test because the latter is more conservative. Some people therefore only use Fisher's exact test when some of the expected counts are too small. But nowadays we can quite easily calculate the exact p-value based on the Pearson statistic, provided it's not a huge table (SPSS can do it). Is there any place for Fisher's exact test then? Tim [[alternative HTML version deleted]]