A pie with twelve slices
The head teacher gets a report. On page one is a pie with twelve thin slices in twelve colours.
She cannot tell which slice is biggest. She puts the report down.
The numbers were right. The picture was wrong. A good picture fits the data, the reader and the job.
Key words
| Word | What it means | Example |
|---|---|---|
| Bar chart | Bars of different heights side by side. You compare amounts. | Students in each year group |
| Line graph | A line that goes up and down over time. | Temperature each hour |
| Pie chart | A circle cut into slices. Each slice is a part of the whole. | How a class travels to school |
| Scatter graph | Dots on a grid. Each dot is one thing with two measures. | Hours of sleep against test mark |
| Audience | The people who will read it. | A head teacher |
| Brief | What the client asked for. It says the job, the reader and the limits. | One page for parents |
| Dashboard | One screen with many pictures of live data. | Attendance today and this term |
| Infographic | A picture with a few big numbers and drawings, for the public. | A poster of school results |
| Average | Add the numbers, then divide by how many there are. | 4, 6, 5 gives 5 |
| Percentage | A part counted out of 100. | 50 out of 100 is 50 percent |
The cells students fill in are left blank in this preview.
Four pictures and what they are for
| Chart | What it looks like | Good for | Not good for |
|---|---|---|---|
| Bar chart | Tall and short blocks side by side | Comparing amounts in groups | Showing a change over many months |
| Line graph | One line going up and down over time | Seeing how something goes up or down over time | Groups with no order, like fruit types |
| Pie chart | A circle cut into slices | A few parts of one whole | Many small parts, or exact numbers |
| Scatter graph | Dots spread over a grid | Seeing if two things go together | Readers who do not know graphs |
The cells students fill in are left blank in this preview.
Quick check: pick the picture
Have a go
Quick check: pick the picture
4 questionsYour answers are marked here and are not kept. A college account keeps every student’s marks.
Worked example: percentages for a pie
| Lunch | Students | Times 5 | Percentage |
|---|---|---|---|
| Pizza | 10 | 10 times 5 = 50 | 50 out of 100: 50 percent |
| Pasta | 6 | 6 times 5 = 30 | 30 out of 100: 30 percent |
| Salad | 4 | 4 times 5 = 20 | 20 out of 100: 20 percent |
| Total | 20 | 20 times 5 = 100 | 100 percent |
The cells students fill in are left blank in this preview.
Worked example: an average
| Step | What we do | Answer |
|---|---|---|
| 1 | Add the marks: 4 + 6 + 5 (the sign + means plus) | 15 |
| 2 | Count the marks | 3 |
| 3 | Divide the total by the count: 15 divided by 3 | 5 |
The cells students fill in are left blank in this preview.
How the table works
There are 20 students. We want a number out of 100. So we multiply by 5, because 20 times 5 is 100.
Ten students become 50. That is 50 percent. The slices must add up to 100 percent. If they do not, check your counting before you draw.
Try it: percentage and average
students = {"Pizza": 10, "Pasta": 6, "Salad": 4}
total = 20
for lunch in students:
share = round(students[lunch] * 100 / total)
print(lunch, share, "percent")
marks = [4, 6, 5]
print("Average:", (4 + 6 + 5) / len(marks))
# Change Pizza to 15 and total to 25. Run it again.
Who reads it? What did they ask for?
The best picture depends on the audience. A scientist can read a scatter graph. A parent at a school event may not.
It also depends on the brief. If the brief says "one page, no numbers", an infographic fits. If it says "show every mark", use a table.