2. Confidence Interval for a difference
between means (x1-x2)
Estimation requirements
1. Both samples are simple random samples
2. Samples are independent
3. Population is at least 10 times larger than the sample size.
4. Sampling distribution of difference between means is
approximately normally distributed
3. 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 SE
4. 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)
