BUS 215 Lecture Notes - Lecture 10: Test Statistic, Minitab

• School: Stony Brook University
• Department: Business Management
• Course: BUS 215
• Professor: Aaron Young- Shin Kim

Document Summary

2 combined number of successes combined sample size. Normality may be assumed if each sample has at least 10 successes and 10 failures, i. e. , if n1p1 10, n1(1 p1) 10, n2p2 10, n2(1 p2) 10 (some textbooks say 5 instead of 10). Test for equality of two means (independent samples) Case 1: known variances or very large samples (z-test) z calc. Case 2: unknown variances assumed equal (pooled samples t-test) n. If both samples are large (n1 30 and n2 30) see situation 1. Case 3: unknown variances assumed unequal (welch"s t-test) t calc x. Welch"s d. f. formula is too hard for hand calculations, but minitab and excel use it. The test statistics in case 2 and case 3 will be the same if n1 = n2. (but decisions may differ due to d. f. 2 with df1 = n1 1 (numerator) and df2 = n2 1 (denominator). The f test is sensitive to population skewness.