*79*

A

**confidence interval for a difference between means**is a range of values that is likely to contain the true difference between two population means with a certain level of confidence.The formula to calculate the confidence interval is:

Confidence interval = (x

_{1}–x_{2}) +/- t*√((s_{p}^{2}/n_{1}) + (s_{p}^{2}/n_{2}))where:

- x
_{1}, x_{2}: sample 1 mean, sample 2 mean - t: the t-critical value based on the confidence level
- s
_{p}^{2}: pooled variance - n
_{1}, n_{2}: sample 1 size, sample 2 size

To find a confidence interval for a difference between two means, simply fill in the boxes below and then click the “Calculate” button.

95% C.I. = [-2.0049, 3.6049]

You can be 95% confident that the interval [-2.0049, 3.6049] contains the true difference between the population means μ

_{1}and μ_{2}.