Charts: Bar, Pie, and Histogram
Numbers alone do not always tell the full story. Charts transform numerical and categorical data into visual patterns that are easier to understand and interpret.
In SPSS, charts are used to: summarize distributions, compare groups, and communicate findings clearly. This lesson focuses on three essential chart types: bar charts, pie charts, and histograms.
Why Visual Representation Matters
Visuals allow analysts and decision-makers to quickly grasp trends and differences that may not be obvious from tables alone.
Charts help you:
- Identify dominant categories
- Compare group sizes
- Observe distribution patterns
- Detect skewness and outliers
Choosing the correct chart type is critical for accurate interpretation.
Bar Charts
Bar charts are used to represent categorical data. Each bar represents a category, and its height corresponds to frequency or percentage.
Bar charts are ideal for comparisons, such as department sizes or response counts.
Example: Employees by Department
| Department | Count |
|---|---|
| IT | 8 |
| HR | 4 |
| Sales | 6 |
A bar chart clearly shows which department has the highest number of employees.
GRAPH
/BAR(SIMPLE)=COUNT BY Department.
Pie Charts
Pie charts represent proportions of a whole. Each slice shows the relative contribution of a category to the total.
Pie charts are best used when the number of categories is small and the goal is to show percentage composition.
However, pie charts are not suitable for precise comparisons between many categories.
GRAPH
/PIE=COUNT BY Department.
This chart shows the percentage distribution of employees by department.
Histograms
Histograms are used for numerical (scale) data. They show how values are distributed across intervals.
Histograms help identify:
- Normal distribution
- Skewness
- Outliers
Example: Distribution of Salaries
| Employee_ID | Monthly_Salary |
|---|---|
| 901 | 42000 |
| 902 | 48000 |
| 903 | 55000 |
| 904 | 62000 |
GRAPH
/HISTOGRAM(NORMAL)=Monthly_Salary.
The histogram shows how salaries are spread across ranges and whether the distribution is symmetric or skewed.
Choosing the Right Chart
Using the wrong chart can mislead interpretation.
- Use bar charts for category comparisons
- Use pie charts for proportions
- Use histograms for numerical distributions
Good visualization improves both analysis quality and communication.
Quiz 1
Which chart is best for categorical comparisons?
Bar chart.
Quiz 2
What type of data is a histogram used for?
Numerical (scale) data.
Quiz 3
Why are pie charts limited in use?
They are hard to compare when many categories exist.
Quiz 4
What does skewness indicate in a histogram?
Asymmetry in data distribution.
Quiz 5
Which chart best shows proportions?
Pie chart.
Mini Practice
Create a dataset with:
- Department
- Monthly_Salary
Perform the following:
- Create a bar chart for Department
- Create a pie chart for Department
- Create a histogram for Monthly_Salary
Use Graphs → Chart Builder or GRAPH syntax to generate the charts.
What’s Next
In the next lesson, you will learn how to create boxplots and scatterplots, which help detect outliers and analyze relationships between variables.