Reconsider Exercises 6.3.26–6.3.29. 

a. If the sample responses had shown more variability in each group (say, SD of 2 in each group) and all else had remained the same as originally, what impact would you expect this to have on the test statistic, p-value, and confidence interval? 

b. Make this change and report the new test statistic, p-value, and confidence interval. Was the impact what you expected?

Data from Exercises 6.3.26

Can waitresses increase their tips simply by introducing themselves by name when they greet customers? A waitress collected data on two-person parties that she waited on during Sunday brunch (with a fixed price of $23.21) at a Charley Brown’s restaurant in southern California. For each party the waitress used a random mechanism to determine whether to give her name as part of her greeting or not. Then she kept track of how much the party gave for a tip at the end of their meal.