SOURCEBOOK

SPSS | Data Analysis

Confidence Intervals

First, enter the data (described elsewhere).
After the data are entered, select the “Analyze → Descriptive Statistics → Explore” option from the main menu.

Obtaining the Exploratory Statistics

A dialogue box will then appear for you to choose the variables of interest.
Select the variables you wish to analyze by clicking on them and hitting the arrow to move them into the “Dependent List” box.
Be sure that “Statistics” is checked. This will limit your output to basic descriptive statistics and confidence intervals.
If you do not wish to alter the default (95%) confidence level, click “OK.” A separate window with the output will appear.

Altering the Confidence Interval

If you wish to alter the width of the confidence interval, select the “Statistics” button.
Another dialogue box will appear where you can change the confidence level. When you are done, click “Continue.” This will return you to the original dialogue box.
After clicking on “OK” in the original dialogue box, a separate window with the output will appear.

Obtaining a Graph of the Confidence Intervals

First, enter the data (described elsewhere).
To obtain a graph, select the “Graphs → Legacy Dialogs → Error Bar” option from the main menu.

Choosing the Graph Layout

A dialogue box will then appear for you to choose the general graph layout of interest.
Click on the box labeled “Simple” (it should then be highlighted).
Then click on the option that states that you want “Summaries of separate variables.”
Click “Define.”

Obtaining the Confidence Interval Graph

A dialogue box will then appear for you to choose the variables of interest to graph.
Under “Error Bars,” move the name(s) of the variable(s) you want to include in the graph.
If you want to change the width of the confidence intervals, type the appropriate percentage in the “Level” box.
After clicking on “OK”, a separate window with the output will appear.