Computing New Variables

In many real-world analyses, the variables you need do not exist directly in the dataset. Instead, they must be created using calculations based on existing variables.

SPSS allows you to compute new variables using mathematical formulas, logical conditions, and built-in functions. This process is called computing new variables.

Why Computing Variables Is Important

Raw data often contains basic measurements, but analysis usually requires derived information.

For example:

• Total score from multiple subjects
• Average monthly spending
• Age calculated from date of birth
• Profit calculated from revenue and cost

Computing variables helps transform raw data into meaningful indicators used for decision-making.

Example Dataset

Consider the following student dataset:

From this dataset, we may want to compute:

• Total score
• Average score

These values do not exist directly but are easy to compute using SPSS.

Computing a New Variable Using the Menu

SPSS provides a simple interface for computing variables.

Typical steps include:

• Select Transform → Compute Variable
• Enter a new variable name
• Define the numeric expression
• Apply the computation

For example, computing the total score:

Total_Score = Math + Science + English

SPSS calculates the value for every case automatically.

Computing Variables Using SPSS Syntax

Syntax allows you to compute variables more precisely and consistently.

COMPUTE Total_Score = Math + Science + English.
COMPUTE Average_Score = Total_Score / 3.
EXECUTE.

This syntax creates two new variables:

• Total_Score
• Average_Score

Using syntax is especially useful when calculations need to be repeated or documented clearly.

Using Conditional Logic

SPSS also allows conditional calculations. This is useful when values depend on rules.

For example, creating a Pass/Fail variable:

IF (Average_Score >= 50) Result = 1.
IF (Average_Score < 50) Result = 0.
EXECUTE.

Here:

• 1 = Pass
• 0 = Fail

Value labels should be added to make output easy to interpret.

Common Mistakes While Computing Variables

Even simple formulas can produce incorrect results if mistakes are made.

• Forgetting parentheses in formulas
• Using incorrect variable names
• Ignoring missing values
• Overwriting original variables

Always verify computed values using descriptive statistics or data inspection.

Quiz 1

Why do we compute new variables?

Quiz 2

Which SPSS menu is used to compute variables?

Quiz 3

What does the EXECUTE command do?

Quiz 4

Why is syntax preferred for repeatable analysis?

Quiz 5

What should you do after computing a variable?

Mini Practice

Create a dataset with the following variables:

• Employee_ID
• Basic_Pay
• Bonus

Compute:

• Total_Pay = Basic_Pay + Bonus

Then create a variable called High_Earner where Total_Pay greater than 50,000 is coded as 1, otherwise 0.

What’s Next

In the next lesson, you will learn how to handle missing data, a critical step for accurate statistical analysis.