Histogram with normal curve
Shows the distribution of a scale variable as bins of equal width, with a normal curve of the same mean and SD for comparison. Panels split it by one or two categorical variables using the same bins.
Menu: Graphs → More charts → Histogram (bin rules, normal curve)…
When should I use it?
- Checking shape, skew and outliers before choosing a test.
- Comparing distributions across groups (panels).
What are the assumptions?
- A scale (interval/ratio) variable.
How do I run it in StatLab?
- Choose the variable.
- Keep the normal curve; choose the bin rule (Sturges is the default; Freedman-Diaconis suits skewed data).
- Optionally add panel row/column variables.
How do I read the output?
| Output | Meaning |
|---|---|
| Bars | Number of cases in each bin. |
| Normal curve | What the histogram would look like if the data were normal with this mean and SD. |
| Mean, Std. Dev., N | Top right of each panel. |
Worked example
On the practice survey dataset (File → Sample dataset), this command — which the dialog's Paste button also produces — runs the procedure:
PROC vizHistogram /x=score /panel='' /panelCol='' /normal=YES /binRule=sturges /niceBins=NO.
Computed by StatLab's validated procedure code when this page was built. The example only illustrates the steps; choose variables that fit your own research question.
What are common mistakes?
- Judging normality from a histogram with very few cases.
- Changing the bin width until the picture looks “normal”.