Exercise 2

The exercises are an integral part of the course, designed to give you confidence in using SPSS. So please do not skip over them. These exercises relate to the topics of the second half of the course: Aggregates, Charts, Compute Variable, Recode into Different Variable, Data Selection.

Aggregates

1. Create an aggregate dataset. Use Data | Aggregate.
2. Set the break variable to be yearam and the aggregated variable to be the sum of number.
3. Create the number of cases, called N_Break.
4. Create the result as a new datasheet called Aggregate.
5. Click into the new dataset. Which year had the most voyages?

Charts

1. Create a histogram chart of yearam against N_Break from the data in your aggregate dataset.
2. What have you plotted?
3. Create another histogram of yearam against number. Does it correlate with the N_Break chart?
4. Can you explain the dips in the graphs around 1745 and 1780?

Compute Variable

1. Use Transform | Compute Variable to create a new variable for the number of men transported for the voyages for which data is available.
2. Call the target variable nomen. The numeric expression should be number * menrat7.
3. Repeat the calculation for the numbers of women and children on the voyages.
4. Use the descriptives function to calculate the mean and standard deviation of the number of men on the voyages.

Recode into Different Variable

1. Use Transform | Recode into Different Variables to set a numeric variable for the islands which were the destinations. Use the optional case selection tool to define the codes (e.g Value = Jamaica; New Value = 1).
2. Call the output variable IsCode.
3. Use the conditional recode process to classify the voyages into Small (up to and including 150 people; value 1) or Large (more than 150 people; value 2), or number missing (value 3).
4. Call the output variable VoySize.
5. How could you determine whether most voyages were large or small? [Hint: you can run a descriptives, but need to deal with the missing values.]

Data Selection

1. Select a case using Data | Select Cases.
2. Use the If… button to select for port of disembarkation Jamaica.
3. Run the selection.
4. Use your filtered file to determine the mean number of slaves delivered per voyage to Jamaica.

Data Selection Contents Summary