Collecting and organising data
Statistics is about collecting, organising and understanding data. A frequency is how many times a value occurs. A frequency table lists each value with its frequency, often using tally marks to count.
| Mark | Tally | Frequency |
|---|---|---|
| 1 | II | 2 |
| 2 | III | 3 |
| 3 | IIII II | 7 |
| 4 | IIII | 5 |
| 5 | III | 3 |
Pie charts
A pie chart shows how a total is shared. A whole circle is 360°, so each item's angle is its share of the total times 360°.
Learners were asked how they travel to school. Change the numbers and watch the slices and angles update.
In a survey of 60 learners, 15 chose football. What angle shows football on a pie chart?
- Fraction of the total.
- Multiply by 360°.
Answer: The football sector is 90°.
Line graphs, frequency polygons and cumulative frequency
A line graph joins points to show how something changes, for example temperature through the day. A frequency polygon joins the middle tops of the bars of a frequency chart. Cumulative frequency is a running total: add each frequency to all those before it. Plotting it gives an S-shaped curve that helps find the median.
| Mark | Frequency | Cumulative frequency |
|---|---|---|
| 1 | 2 | 2 |
| 2 | 3 | 5 |
| 3 | 7 | 12 |
| 4 | 5 | 17 |
| 5 | 3 | 20 |
Key terms
- Frequency
- How many times a value occurs.
- Tally
- Marks used to count, grouped in fives.
- Pie chart
- A circle divided into sectors showing shares of a total.
- Cumulative frequency
- A running total of frequencies.
Summary
- Organise data in a frequency table using tallies.
- Bar charts show frequency by height; pie charts show shares by angle.
- Pie angle = frequency ÷ total × 360°.
- Cumulative frequency is a running total and ends at the total.