Data Manipulation II Transforming, Recoding, and SplittingGrouping

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Data Manipulation II Transforming, Recoding, and SplittingGrouping

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To create averages of existing variables. To rescale existing variables ... Into Different Variables option - create a new variable with the recoded values. ... – PowerPoint PPT presentation

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Title: Data Manipulation II Transforming, Recoding, and SplittingGrouping

1
Data Manipulation IITransforming, Recoding, and
Splitting/Grouping

SPSS Training
Thomas Joshua, MS
July 2008

2
Lecture Overview

Transformation (computing) of Data
Recoding
Splitting/Grouping

3
Transformation (computing) of Data

SPSS has very powerful capabilities for creating
new variables as a function of existing
variables, for example
To create averages of existing variables
To rescale existing variables
To compute difference scores by subtracting one
variable from another

4
Computing A New Variable

Target Variable - new variable name.
Numeric Expression - defining the new variable,
essentially giving SPSS a formula.
The variables in the Numeric Expression need to
be either existing variables or numbers.
Specify the Type and Label for the new Variable.

5
Conditionally Computing A New Variable

Variables can also be computed conditionally.
For instance, if in the above example, you were
only interested in the change in salaries for
people who began working for the company within
the last six years.
If button
(optional case selection condition)

6
Transforming An Existing Variable

For example, the variable jobtime represents
months of experience on the job, but we may wish
to analyze data in terms of years on the job
Give a new variable name or keep the existing
name for the Target Variable

7
Recoding Variables

Another way to modify the values of existing
variables in your dataset. In the Data Editor
Transform -gt Recode

Into Same Variables option - changes the values
of the existing variables.
Into Different Variables option - create a new
variable with the recoded values. (not overwrite
your original data)
Both options are essentially the same, except
that recoding into a different variable requires
you to supply a new variable name.

8
Recoding VariablesCategories to Categories

For example, the variable jobcat codes an
employee's status in three categories, but for a
particular analysis you may want to combine two
of these classifications into a single category.
The original coding was
Clerical 1 -gt 1
Custodial 2 -gt 2
Manager 3 -gt 2

9
Recoding Variables
Input variable -gt Output variable -gt Change
bottom -gt Define the old and new values
10

With System-missing selected
Without System-missing selected

11
Recoding VariablesNumeric to Categories

Recode the continuous variable to the categorical
variable
Useful in cross-tabulation
Group ranges of the variable into categories
For example, we need to code an employee's
current salary into two categories as the
following

Less than or equal to 27,000 (Low) -gt 1
More than 27,000 (High) -gt
2
12
Recoding VariablesNumeric to Categories
13

Where is the value 27,000?

How about if there are more than 2 groups?

14
Splitting/Grouping

In some situations, you may want to perform the
same analysis on different groups within the same
dataset.
Analyses such as these can be conducted by first
selecting the Split File function from the Data
menu in the Data Editor
Data -gt Split File...

15
Splitting/Grouping

If you select the option to "Sort the file by
grouping variable," SPSS will run the "Sort File"
command in the background.

Because the split file command remains in effect
indefinitely, you should reset this option when
you no longer want a split file analysis.
16
Splitting/Grouping

The Compare groups and Organize output by groups
result in the same values in the output,
regardless of the analysis being performed, but
they differ in the way in which the output is
presented.
Compare groups

SORT CASES BY gender . SPLIT FILE LAYERED BY
gender .
17
Splitting/Grouping