Difference Between Two Means Population means, independent samples o and 02 known Use a z test statistic Use S to estimate unknown o, o,and o2 unknown use a t test statistic and pooled standard deviation Statistics for Managers Using Microsoft Excel Chap9-8 Statistics for Managers Using Microsoft Excel Chap 9-8 Difference Between Two Means Population means, independent samples σ1 and σ2 known σ1 and σ2 unknown Use a Z test statistic Use S to estimate unknown σ , use a t test statistic and pooled standard deviation