Histograms — Data, 14–17 years
See how numerical data are distributed by grouping values into intervals. Data, 14–17 years.
What a histogram shows
A histogram shows how many numerical values fall inside each interval, such as 0–10 or 10–20 minutes. Touching bars mean the intervals join continuously; the area or height represents how much data is there, depending on the scale. It reveals the shape of a distribution at a glance.
Why group values
A long list of measurements is hard to read and compare. Histograms were developed to compress many observations into a picture without throwing away the overall pattern. The problem they solve is not finding one exact value, but seeing where values cluster, spread out or leave gaps.
Building one
Suppose 20 journey times, in minutes, are grouped into 0–10: 3 journeys, 10–20: 8, 20–30: 6, and 30–40: 3. Draw four touching bars with those heights. The tallest bar says the 10–20 interval is the modal class; it does not say every journey lasted 15 minutes.
The trap
People often read each bar as if all values inside it were equal to its midpoint. That feels natural because a grouped interval has one label, but the original values may be spread anywhere inside it. A histogram shows a range of possibilities, not the exact locations of every observation.
Where it appears
Histograms are used for rainfall totals, delivery times, test scores, machine part sizes and sensor readings. A factory can see that most parts are near the target size, while a long tail may reveal a production problem. The picture is useful, but the interval choices can change what stands out.
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