DEFINITION of 'TTest'
A statistical examination of two population means. A twosample ttest examines whether two samples are different and is commonly used when the variances of two normal distributions are unknown and when an experiment uses a small sample size. For example, a ttest could be used to compare the average floor routine score of the U.S. women's Olympic gymnastic team to the average floor routine score of China's women's team.
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BREAKING DOWN 'TTest'
The test statistic in the ttest is known as the tstatistic. The ttest looks at the tstatistic, tdistribution and degrees of freedom to determine a p value (probability) that can be used to determine whether the population means differ. The ttest is one of a number of hypothesis tests. To compare three or more variables, statisticians use an analysis of variance (ANOVA). If the sample size is large, they use a ztest. Other hypothesis tests include the chisquare test and ftest.

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