The use of Z or t again depends on whether the sample sizes are large (n 1 > 30 and n 2 > 30) or small. The confidence interval will be computed using either the Z or t distribution for the selected confidence level and the standard error of the point estimate. The point estimate for the difference in population means is the difference in sample means: In the two independent samples application with a continuous outcome, the parameter of interest is the difference in population means, μ 1 - μ 2. We could begin by computing the sample sizes (n 1 and n 2), means ( and ), and standard deviations (s 1 and s 2) in each sample. Both of these situations involve comparisons between two independent groups, meaning that there are different people in the groups being compared. For example, we might be interested in comparing mean systolic blood pressure in men and women, or perhaps compare body mass index (BMI) in smokers and non-smokers.
There are many situations where it is of interest to compare two groups with respect to their mean scores on a continuous outcome. Confidence Interval for Two Independent Samples, Continuous Outcome
