chapter  10
2 Pages

Draw a Happy Face?

The dining parties that had a happy face drawn on their checks had these percentage tips (that is, the percentage left by each dining party): 1

For the data in Table 1, the mean tip was 18%. (You may recall from earlier in this book, the mean is a widely used average.)

For the group without happy faces, these are the percentage tips left by the dining parties:

For the data in Table 2, the mean tip was 21%. Thus, on the average when the waiter did not draw a happy face, he got

higher tips (21 %) than when he did draw a happy face (18%). However, it is clear from the data that the averages don't tell the whole story. In fact, reporting only the averages might be misleading because there is tremendous variation under

eachoftheconditions,andthiatoverlapinthepercentagesunderthetwoconditions.thateventhoughTable1 hasalowermean(18%),everleishigherthanthethree lowestpercentagetipsinTable2(thatis,thethreepartiesthatleft0%).