The idea, step by step
What kind of answer will you collect?
Data are recorded answers or observations. Category data give a name or group, such as favourite fruit. Number data give a count or measurement, such as books borrowed or height in centimetres. Decide what the variable is before choosing how to record it.
A numeral can still be a label: bus route 7 is a route name, not seven buses. Ask whether adding those numbers would have a useful meaning.
Check before using the records
Validation means checking that a record fits the question and the agreed units. Look for missing answers, impossible entries and unusual values. Check the original measurement or ask the person who recorded it. Do not silently change or delete a value just because it is different.
In a one-answer fruit survey, category counts should add to the number who answered. If 20 people answered but the counts total 21, check for a double-counted response.
| Fruit | Votes |
|---|---|
| Apples | 8 |
| Bananas | 6 |
| Oranges | 4 |
| Pears | 2 |
A common trap
Every answer written as a numeral is number data.
Instead: A number used only as a name, such as a shirt number, is a category label.
See the thinking
Numbers used as labels
Classify favourite game, number of pets and bus route number.
- Favourite game is a category because it names a choice.
- Number of pets is a count, so it is number data.
- A bus route number identifies a route. It is category data, not a count of buses.
An entry to check
Plant heights are recorded as 8, 9, 85, 10, 9 centimetres. What should happen before graphing?
- All entries are numbers, but 85 is much larger than the others.
- Check the recorded unit and remeasure that plant if possible.
- Correct the entry only when evidence shows a mistake; keep a record of the correction.
Check your understanding
Is the number of library books borrowed category data or number data?
Show answer
Number data: it is a count.
Four books means four items. Counts can be meaningfully totalled.
Your turn
6 questions · 9 marks · Work at your own pace.
Read the questions online
- Classify favourite sandwich filling as category data or number data.1 mark
- Classify the length of a pencil in centimetres.1 mark
- Classify a football player's shirt number.1 mark
- A survey has 18 answers. Category counts are 6, 5 and 8. What needs checking?2 marks
- Reading times are recorded as 4 hours, 5 hours and 300 minutes. Explain why the units matter.2 marks
- A data sheet has a blank height. Should it be entered as zero? Explain.2 marks
Read the worked solutions
Equivalent correct methods earn the corresponding marks. Include units where asked.
- Classify favourite sandwich filling as category data or number data.1 mark
The answer names a kind of filling.
Category data. - Classify the length of a pencil in centimetres.1 mark
Length is a measurement with a unit.
Number data. - Classify a football player's shirt number.1 mark
It identifies a player; it does not measure the player.
Category data. - A survey has 18 answers. Category counts are 6, 5 and 8. What needs checking?2 marks
6 + 5 + 8 = 19.
Check for an extra or double-counted response; do not remove one without evidence.
The counts total 19, one more than the 18 answers. - Reading times are recorded as 4 hours, 5 hours and 300 minutes. Explain why the units matter.2 marks
There are 60 minutes in an hour.
300 ÷ 60 = 5.
Use one agreed unit before comparing; 300 minutes equals 5 hours. - A data sheet has a blank height. Should it be entered as zero? Explain.2 marks
Check or remeasure if possible.
If it cannot be obtained, label the measurement missing.
No. A missing measurement is not a measured height of zero.
Curriculum reference & lesson scope
Australian Curriculum v9 / SA Curriculum 2026
Data types/validation; mode; suitable displays; line graphs; statistical investigations.
Official curriculum source ↗