Tables and bar charts

Q: In the injury survey, where did the most injuries happen? (hallway 12, playground 25, gym 18, classroom 7)

Playground — The playground has the most, with 25.

Q: When you read a bar chart, what should you look at first?

How much one step on the scale is worth — If you don't check how much one step on the scale is worth, you will read the numbers wrong.

Q: What is the difference between injuries in the hallway and in the classroom? (hallway 12, classroom 7)

5 injuries — 12 − 7 = 5 injuries.

Q: What should you do when you see a graph whose up-and-down axis does not start at 0?

Be careful — the gaps may look bigger than they really are — When a graph doesn't start at 0, small differences look big. Check the scale first.

Q: After you have drawn a graph, what matters most?

Deciding what to do about it — A graph is a tool for making decisions. It only means something once it leads to an action.

Where this is used

A table full of numbers is hard to read at a glance. Turn it into a graph and you can see straight away what is big, what is small, what went up and what went down. Meetings at work and stories on the news are explained with graphs almost every time.

Key points

First, tidy your data into a table

Whatever you counted, start by making a table with two columns: the kind of thing, and how many. While you count, make tally marks in groups of five — that way you are much less likely to miss one. Build the table first, then draw the graph from it.

A bar chart compares how much of each

The length of each bar stands for a number. The longer the bar, the bigger the number. Before you read any bar, always check the scale first: how much is one step on the axis worth?

Where injuries happened (one month)

The playground has the most. So we can decide to check the playground more often.

You draw a graph so you can decide what to do

The point of a graph is not to look neat. It is to help you answer the question "so what should we do?" For the graph above, the answer is "keep a closer eye on the playground." Only when you can say that have you really used the graph.

Watch the scale

The very same numbers can leave a different impression depending on the scale you choose. When a graph does not start at 0, small gaps look huge. Whenever you see a graph on the news, get into the habit of checking whether the up-and-down axis starts at 0.

Same numbers, but they can look different

When you draw it from 0, there is hardly any difference at all.

Check yourself 5questions

Tap an option to check

Q1 In the injury survey, where did the most injuries happen? (hallway 12, playground 25, gym 18, classroom 7)

Q2 When you read a bar chart, what should you look at first?

Q3 What is the difference between injuries in the hallway and in the classroom? (hallway 12, classroom 7)

Q4 What should you do when you see a graph whose up-and-down axis does not start at 0?

Q5 After you have drawn a graph, what matters most?

Jobs that use this

Every job uses this. The ones below are just where it shows up most.

Local government worker $52k

Shop marketing planner $70k

News reporter $60k

Local government worker$52k

They graph where accidents and injuries happen most, then decide where to put a new traffic light or street lamp. A graph can move where a whole town spends its money.

Maths used: Tables and graphsProportionsStatistics

Shop marketing planner$70k

They graph which products sold, and when, then decide what to order next. The decision comes from the graph, not from a hunch.

Maths used: Tables and graphsAveragesProportions

News reporter$60k

They turn numbers into graphs so readers can understand them. They also need a sharp eye for other people's graphs, to catch the trick of a scale that doesn't start at 0.

Maths used: Tables and graphsStatistics