Dot Plots and Histograms

A dot plot puts one dot above each value, stacked when a value repeats.

A histogram groups first

Values are collected into bins — 0 to 9, 10 to 19 — and each bar shows how many fell in that bin.

Which to use

A dot plot suits a small set with few different values. A histogram suits a large or spread-out set.

What a histogram hides

Once values are binned you can no longer see the individual numbers. That is the price of the tidier picture.

Dot plots show every value

A dot plot puts one dot above the number line for each data point. Nothing is lost — you can read every individual value back off the plot. That makes them ideal for small data sets where each observation matters.

Histograms group into intervals

A histogram sorts values into intervals — 0 to 9, 10 to 19 — and draws a bar for how many fall in each. Individual values are lost, but a large data set becomes readable. The trade is detail for clarity.

A histogram is not a bar chart

Bar charts show categories and their bars have gaps; histograms show number intervals and their bars touch, because the intervals are continuous. The touching bars are a signal that the horizontal axis is a number line.

The interval width changes the picture

The same data plotted with intervals of 5 and of 20 can look quite different — one showing structure, the other a single lump. Choosing the interval is a real decision that affects what a reader concludes, and it should be made honestly.