Suppose you are researching dieting behaviour. You have a theoretical basis for believing that women go on diets more often than men. However, in your study, you investigated not only dieting behaviour but also other aspects of personal care. You surveyed both men and women. In terms of the number of times a respondent has been on a diet, you are only interested in the answers given by women. In this case, you can 'exclude' the men in SPSS. For this exercise, use Summo7.sav.

a. Generate a frequency table of the variable g2a (Personal care - dieted in the past 12 months). Do not exclude the men yet! Compare your syntax to the correct answer.

b. What percentage of the respondents has dieted in the past 12 months? Do not exclude the men yet!

c. Now use Select Cases to select only the women, and compare your syntax to the correct answer.

d. Generate the frequency table again. What percentage of the women has dieted in the past 12 months?

e. Do not select every woman, only the younger ones (up to the age of 34 years). Compare your syntax to the correct answer.

f. What percentage of the younger women has dieted in the past 12 months?

g. Select all the younger women who use make-up every day (variable 'g15bp9'). To select age, use the 'greater than' or 'less than' signs. Compare your syntax to the correct answer.

h. What percentage of the younger women who use make-up every day has been on a diet in the past 12 months?

Hints

1 How do I select units of analysis? Sometimes, you only want to include in your study units of analysis with a certain characteristic. For example, you want to make a statement only about women, or only about PvdA voters, or only about people who read de Volkskrant. In that case, you can indicate in SPSS that you want to exclude from your analyses every unit that does not have a certain characteristic.

To do this, use the Select Cases command under Data. The 'Select Cases' screen now appears.

Select the 'Select if condition is satisfied' option and click the 'IF...' button. Another screen now opens: 'Select Cases: if'. In the empty field, indicate which units of analysis (cases) should be selected. This can be done by using the names of the variables in the left-hand list and the various mathematical symbols and digits at the bottom right.

Suppose that you want to select only male respondents. 'Gender' is measured by variable v1, where 'male' has the value 1. In other words, you only select units of analysis that meet the requirement of scoring 1 on the v1 variable. Then click Continue to return to the previous screen, and then click OK. In the Data View, you can now see that SPSS literally crosses out every unit of analysis that does not meet the condition of being male (i.e. all the women). Every analysis you conduct now only includes men, and no longer women.

Suppose that you want to select only men, but that they should also meet the condition that they work full-time. Part-time/full-time working is measured in variable 'v2', where the value of 1 represents part-time and 2 full-time. We indicate this by putting the '&' symbol after the selection 'v1 = 1', and then 'v2=2': we only want to select men with a full-time job.

Using Select Cases, we can also indicate that the units of analysis should have one or other of the characteristics. Suppose that we want to select only those people who either have a part-time job ('v2 = 1') or who watch television for less than four hours (measured in variable v3). We indicate 'or' by placing a vertical column ('|') between the variables, or by typing the word OR between them.

In all subsequent analyses, the answers of the respondents who do not meet the specified conditions are disregarded. You can undo the selection (actually a filter) by going back to the Select Cases menu and selecting the All Cases option.