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University of Massachusetts at Boston T-TEST Research Methods University of Massachusetts at Boston ©2006 William Holmes

T-TEST: COMPARING TWO GROUP MEANS Set criterion (alpha level). Check group frequencies, means, and standard deviations. Compare means for each group. Examine t-value, degrees of freedom, and significance probability. If probability smaller that alpha level, difference is significant.

EXAMPLE 1: t-test Mental Health by Sex Males Females 29.7 31.8 25 27 3.96 4.11 . Mean N Std. Dev. Difference of Means=2.1 Are women healthier than men?

EXAMPLE 1(cont’d.): t-test Mental Health by Sex Males Females 29.7 31.8 25 27 3.96 4.11 . Mean N Std. Dev. Difference of Means=2.1 t=1.89, d.f.=48, P=.06 Answer: Women are not healthier than men.