title: Statistics for clinicians. 2. Nominal data (I).
abstract: Nominal data consist of items assigned to well defined classes. They are presented as a proportion or percentage of the total. From a sample percentage we can estimate the population percentage with a desired degree of confidence, using standard error of the percentage as a measure of chance variation. We can compare the difference in percentage between two groups by means of the z-test or the chi-square test. If the number of observations is less than 40, Fisher's test is preferable to the chi-square test. When chi-square test is done on 2x2 tables, Yates' correction is recommended. For tables larger than a 2x2, Yates' correction is not used. When testing paired data for significance of difference, we need to use McNemar's modification of Chi-square test. Chi-square test is useful not only to test the significance of differences but also to test the significance of an association between attributes.
authors.affiliation: Pfizer Limited, Bombay.
authors.forename: A S
authors.initials: AS
authors.lastname: Nanivadekar
authors.forename: A R
authors.initials: AR
authors.lastname: Kannappan
mesh_terms: D000900:Anti-Bacterial Agents / Q000627:therapeutic use; D016009:Chi-Square Distribution; D005260:Female; D006801:Humans; D008297:Male; D008433:Mathematics; D010003:Osteoarthritis / Q000145:classification; D010033:Otitis Media / Q000188:drug therapy; D013223:Statistics as Topic
chemical_list: D000900:Anti-Bacterial Agents