Confidence Intervalfor a

Difference between Means

Confidence Interval for a difference between means (x1-x2)

Estimation requirements1. Both samples are simple random samples2. Samples are independent3. Population is at least 10 times larger than the sample size.4. Sampling distribution of difference between means is

approximately normally distributed

How to find the confidence interval for the difference between two means

1. sample statistic (use difference between sample means to estimate difference between population means)

2. CL (90%, 95%, 99%)3. ME= CV x SD or ME= CV x SE4. Specify CI: sample statistic + ME written as: (Sample Stat – ME, Sample Stat + ME)

**for t-score, need degrees of freedom: n1 +n2-2

σ(x1-x2) = ** Can be found on the table under two-sample (difference of sample means)