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3.成组设计的两样本均数的比较

——成组t检验（two-sample t-test for independent samples)：例：X1?X2t?SX1?X2SX1?X2?S(?1n12C1n21)2S2CX???X???2121n1??X?2222??X?22n2n1?n2?2(n1?1)S?(n2?1)S ?n1?n2?2??n1?n2?229

某医生测得18例慢性支气管炎患者及16例健康人的尿17

酮类固醇排出量（mg/dl）分别为X1和X2，试问两组的均数有无不同。

X1：3.14 5.83 7.35 4.62 4.05 5.08 4.98 4.22 4.35 2.35

2.89 2.16 5.55 5.94 4.40 5.35 3.80 4.12

X2：4.12 7.89 3.24 6.36 3.48 6.74 4.67 7.38 4.95 4.08

5.34 4.27 6.54 4.62 5.92 5.18

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Group Statisticsgroupx12N1816Mean4.4545.299Independent Samples TestLevene's Testfor Equality ofVariancesStd.Deviation1.3241.382Std. ErrorMean.312.346t-test for Equality of Means95% ConfidenceInterval of theDifferenceFxSig.tdfSig.Mean(2-tailed)DifferenceStd. ErrorDifferenceLowerEqual variancesassumedEqual variancesnot assumedUpper.225.638-1.81832.078.079-.844-.844.464.466-1.790-1.794.102.105-1.81331.16方差齐性检验SPSS3132