Comparing Two Means with Confidence Intervals A confidence

Comparing Two Means with Confidence Intervals A confidence interval will estimate the difference of population means (m 1 – m 2). Test statistic ± critical value ∙ (standard error) z* t* Example: Do low fat cookies have the same average number of chocolate chips as regular? In a random sample of 25 cookies each, regular cookies had a mean of 16. 3 chips with a standard deviation of 2. 29 and low fat cookies had a mean of 15. 2 with a standard deviation of 3. 25. The distributions were found to be fairly normal. Estimate the difference in the average number of chips between regular cookies and low fat cookies for all cookies of this brand with a 95% confidence interval.

Comparing 2 sample proportions with Confidence Intervals A confidence interval estimates the difference of population proportions (p 1 – p 2). Test statistic ± z*(standard error) Example: An airline wishes to estimate the difference in the proportion of male first class passengers on their transcontinental flights compared to their intercontinental flights. A set of random flights of each type were chosen. Out of 99 transcontinental passengers, 73 were male. Out of 91 intercontinental passengers, 56 were male. Estimate the difference in these proportions of male passengers for all flights with a 95% confidence interval.