Independent Samples t test

The independent samples t test is a hypothesis test of whether the means of a continuous outcome differ between two unrelated groups.

독립표본 t검정은 서로 관련 없는 두 집단 사이에 연속형 결과변수의 평균이 다른지를 검정하는 방법이다.

How do I test whether the means of two independent groups differ?

서로 독립인 두 집단의 평균이 다른지 어떻게 검정하나요?

The independent samples t test compares the mean of a continuous outcome between two separate groups, such as treatment and control. When group variances are unequal, Welch's version of the test is the standard choice.

When to use Independent Samples t test

• One continuous outcome and a grouping variable with exactly two independent groups
• Comparing treatment and control, or two demographic groups, on a mean
• Roughly normal outcomes within each group or reasonably large groups

When to use something else

• Three or more groups; use one-way ANOVA
• Skewed outcomes in small samples or ordinal outcomes; use the Mann-Whitney U test

Assumptions and requirements

• Independent observations
• Approximately normal outcome within each group
• Equal variances for Student's version; Welch's version relaxes this

What the analysis reports

• t statistic and degrees of freedom
• p-value
• Group means and standard deviations
• Mean difference with 95% confidence interval
• Cohen's d

How to report it

[Group 1] (M = [value], SD = [value]) scored higher than [Group 2] (M = [value], SD = [value]), t([df]) = [value], p = [value], d = [value].

Related methods

• Welch's t Test
• Mann-Whitney U Test
• Paired Samples t Test

Run Independent Samples t test on Quorant