Clinical Trials

❘❙❚■ Chapter 19 | Comparison of MeansTable 5. The individual differences in FEV 1between pre- and posttreatment in group A, together with summarystatistics for the paired t-test.Subject Treatment Pretreatment Posttreatment DifferenceFEV 1(mL)FEV 1(mL)4 A 1797 2215 4186 A 2344 3117 7737 A 1719 2051 33210 A 1719 1969 25011 A 2016 2264 24812 A 2188 3117 93016 A 2266 2953 68818 A 2031 2379 34819 A 2500 3035 53522 A 1797 2215 41823 A 1875 2264 38924 A 1875 2215 340n 12X d472.4S 216.4SE 62.5S = standard deviation; SE = standard error.Under the null hypothesis, the test statistic in equation (4) is distributed as thet-distribution with n – 1 degrees of freedom [2,5]. Therefore, there is evidenceagainst the null hypothesis of H 0at the α level of significance if |t| ≥ t α/2,n–1. Thecorresponding 100(1 – α)% CI can be calculated from the following equation:X d± t α/2,n–1× SE(X d) (5)Table 5 displays the individual differences in FEV 1between pre- andposttreatment in group A, together with some summary statistics required for thepaired t-test. Using these statistics, the paired t-test statistic is given by:Xt = d= 472.4 = 7.56SE(X d) 62.5206