244 Fundamentals of Statistics
the p values returned by the t statistic will still be fairly accurate. As long as
the distribution of the data does not violate the assumption of normality in an
extreme way, you can use the t distribution with confi dence.Applying the t Test to Paired Data
The t distribution becomes useful in analyzing paired data, where observa-
tions come in natural pairs and you wish to explore the difference between
two pairs. For example, a doctor might measure the effect of a drug by mea-
suring the physiological state of patients before and after administering the
drug. Each patient in this study has two observations, and the observations
are paired with each other. To determine the drug’s effectiveness, the doctor
looks at the difference between the before and after readings.
The Labor workbook contains data on the percentage of women in the
workforce in 1968 and 1972 taken from a sample of 19 cities. The workbook
contains the following variables:Table 6-3 Data on percentage of women in the workforce
Range Name Range Description
City A2:A20 The name of the city
Year_68 B2:B20 The percent of women in the workforce in 1968
Year_72 C2:C20 The percent of women in the workforce in 1972
Diff D2:D20 The change in percentage from 1968 to 1972 for each city
To open the Labor workbook:1 Open the Labor workbook from the Chapter06 folder.
2 Save the fi le as Labor Analysis to the same folder. The workbook
appears as shown in Figure 6-11.