Read the axes
The horizontal axis is numeric and continuous or ordered. The vertical axis may show count, frequency, proportion, or density. With unequal bin widths, bar area, not height alone, should represent frequency.
Describe:
- where most observations lie;
- total and central spread;
- left or right skew;
- one or more modes;
- gaps and heaping;
- unusually long tails or isolated bins.
Bin width changes the story
Wide bins hide local structure. Narrow bins amplify sampling noise. Freedman and Diaconis proposed a data-dependent bin-width rule using the interquartile range and sample size, but it remains a construction choice rather than a unique true histogram.2
Inspect several defensible bin widths and preserve meaningful boundaries. Do not choose bins solely to make a preferred mode appear.
Unlike a bar chart, a histogram represents numeric intervals whose bars normally touch. A density curve smooths the data and adds a bandwidth decision. Box plots compress quartiles and whiskers; skewness and kurtosis provide numeric shape summaries; scatter plots show relationships between two variables.
A defensible reporting sentence
“The distribution was right-skewed with one main mode and a long upper tail. The feature remained visible across several bin widths, so it was not an artifact of one histogram setting.”