spss 2

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DataModifications.ppt
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Transforming data to fit the application

Introduction to Data Modification

  • Adapting data to fit the application

Recode existing varaibles

Compute a new variable

Selecting cases from a data file

Splitting the data file into groups

Selecting cases and splitting files are not data modification, but are included as steps preceding descriptive and inferential statistical analysis procedures.

Recode Variables

  • Variables are recoded for two reasons

1. To modify certain values of a variable

2. To group certain values into a single value.

When recoding, two options are available

1. Recode into same variable

2. Recode into different variables.

Recoding into Same Variables

  • When using this option, the variable keeps the same name and labels, with the new values in the same column.

  • Original data is lost
  • No way to undo the action
  • Not advisable method

This method retains the original variables

Values are added to the data file under a new variable name in the first empty column of the file.

Transform > Recode into different variables

Recode Variables

Recode Variables Create new variable

Recode Variables Create new value

Select Variable View and provide names for the two values of the “youngold” variable.

1 = young

2 = old

New variable is now ready to use.

Recode Variables Name new value

SPSS provides a way to create new variable from a combination of other existing variables.

For example, if we have data measuring computer skills on several different indicators. We could add the scores similar to an interval scale to achieve a ranking as in a Likert scale.

Transform > Compute Variable

Create New Variable

Create New Variable

Select Cases

  • Used when analysis is run only on a selected subset of cases in the data file.
  • Data > Select Cases

Select Cases

Select Cases Filter remains on (lower right) until removed

Split Files

Used to separate the file into groups, such as male and females.

Data > Split File

Split Files

Analysis proceeds now based on the two separate groups.

Go to Data > Split File > Reset

Recombines the data file into one group