Statistics · Histograms
Chapter 1 · 3
The idea
Histograms & frequency density
Why a histogram with unequal class widths cannot use frequency as the bar height, and how the rule "area = frequency" fixes it: height = frequency ÷ class width. Drawing the bars, reading a frequency back off a bar as density × width, and why the axis must say "Frequency density".
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Statistics · Histograms
Histograms & frequency density
Why a histogram with unequal class widths cannot use frequency as the bar height, and how the rule "area = frequency" fixes it: height = frequency ÷ class width. Drawing the bars, reading a frequency back off a bar as density × width, and why the axis must say "Frequency density".
Why it works
A bar chart it is not
A bar chart is for categories — favourite sport, eye colour — and its bars stand apart, because there is nothing in between "football" and "netball". A histogram is for continuous data grouped into classes, and its bars touch, because the data runs straight on from one class into the next. That would be cosmetic if every class were the same width — but in real data they usually aren't: you group finely where values are packed and coarsely out in the tail.Keep reading — free
The rest of the explanation, plus 3 worked examples you step through move by move.
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