Tham khảo tài liệu '100 statistical tests phần 4', ngoại ngữ, ngữ pháp tiếng anh phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | THE TESTS 67 Test 29 The Link-Wallace test for multiple comparison of K population means equal sample sizes Object To investigate the significance of all possible differences between K population means. Limitations 1. The K populations are normally distributed with equal variances. 2. The K samples each contain n observations. Method The test statistic is nw x Kl k ỵ Wi x i 1 where wi x is the range of the x values for the ith sample w x is the range of the sample means n is the sample size. The null hypothesis ỊX1 ỊX2 K is rejected if the observed value of KL is larger than the critical value obtained from Table 10. Example Three advertising theme tunes are compared using three panels to assess their pleasure using a set of scales. The test statistic D is computed as and then the three differences between the ranges of means are also calculated. Tunes 3 and 2 differ as do tunes 3 and 1 but tunes 1 and 2 do not. Numerical calculation n 8 w1 x 7 w2 x 6 w3 x 4 K 3 W1 x W2 x W3 x K _ nw x _ 8 - _ 47 Kl 7 6 4 . 7 ỵy x i 1 Critical value K8 3 Table 10 . Reject the null hypothesis of equal means. 68 100 STATISTICAL TESTS Using K8 3 the critical value for the sample mean differences is D Wi x X 17 n 8 . Since w1 w2 x less than D w3 W w2 x greater than D w3 x w1 greater than D reject the null hypothesis 1 3 and 2 I 3. THE TESTS 69 Test 30 Dunnett s test for comparing K treatments with a control Object To investigate the significance of the differences when several treatments are compared with a control. Limitations 1. The K 1 samples consisting of K treatments and one control all have the same size n. 2. The samples are drawn independently from normally distributed populations with equal variances. Method The variance within the K 1 groups is calculated from S2 S0 S1 ----- SK K - 1 n - 1 where S2 is the sum of squares of deviations from the group mean for the control group and sj is a .
