# R - (dependent|paired sample) t-test

• The Mean of differences is the point estimate
• The confidence interval is the interval estimate around the mean difference (not around the mean of the samples)

## 3 - Package

### 3.1 - stats

#### 3.1.1 - dependent t-test

t.test(data$pre, data$post, paired = T)
	Paired t-test

data:  data$pre and data$post
t = -9.0089, df = 39, p-value = 4.511e-11
alternative hypothesis: true difference in means is not equal to 0
95 percent confidence interval:
-2.41843 -1.53157
sample estimates:
mean of the differences
-1.975 
$$\text{Cohen's d} = \frac{\text{Mean of difference scores}}{\text{Standard deviation of difference scores}}$$
cohensD(data$post, data$post, method="paired")
[1] 0.4485912