Bar charts, tables and what they hide
Maths · Key Stage 2 · The School
Read the scale before you read the bars
The first thing to look at on a bar chart is not the tallest bar — it is the numbers up the side. If the gaps go up in twos, a bar reaching the third mark is 6, not 3. Reading the scale first prevents the most common wrong answer in the whole topic.
Two-step questions are the ones worth marks
“How many chose red?” is one step. “How many more chose red than blue?” is two: read both bars, then subtract. “How many altogether?” means read every bar and add. The question word tells you which, so underline it before you start counting.
Tables hold the same data without the picture
A table is the same information as a bar chart, arranged in rows and columns. It is more exact — you read a number rather than judging a height — but it is slower to compare. That is the whole trade: charts show shape, tables show values.
A chart can be honest and still mislead
If the scale starts at 50 rather than 0, a bar of 54 looks four times taller than one of 51, though the real difference is tiny. Nothing has been faked; the picture is simply doing something the numbers do not. Always check where the scale begins before believing a gap you can see.
What the chart never had
Here is an imagined class with made-up numbers. In a class of 28, each child votes once for a favourite lunch. The chart shows pizza 12, pasta 8 and jacket potato 6. Sam says, "Most of the class chose pizza." We check this in three steps. Step 1: most means more than half. Half of 28 is 14, and pizza has only 12. Step 2: add the bars. 12 + 8 + 6 = 26, so 2 votes are missing. If both were for pizza, that makes 14, which is still only half. So most cannot be true, whatever the missing votes say. No other choice can pass 12 either, because pasta with both would reach only 10. So pizza stays on top. Step 3: only this class voted, so the chart cannot show what the whole school wants. The honest claim is that pizza has the most votes in this class, but no more than half of the class chose it.