Ask 30 pupils, not 1,200
A school wants to know how pupils get to school. Asking all 1,200 takes weeks. Asking 30 takes a day.
But the 30 must stand for everyone. If they are all from one bus, the answer will be wrong.
Key words
| Word | What it means |
|---|---|
| Dataset | a collection of related data about one subject |
| Population | all the items you want to learn about |
| Sample | the smaller group you pick from the population |
| Representative | a sample that reflects the whole population |
| Random sampling | every item has an equal chance of being picked |
| Bias | a built-in unfairness that skews a result |
| Seed | a starting number that makes a random choice repeatable |
The cells students fill in are left blank in this preview.
By the end of this lesson
Note
I can prepare a dataset and take a random sample from it.
Starter
Have a go
Starter
3 questionsYour answers are marked here and are not kept. A college account keeps every student’s marks.
Identify the purpose and requirements
Ask what the sample is for and what it must be like. What is the population? How big must the sample be? How exact must the answer be?
A representative sample reflects the whole population. A sample that does not is said to show bias.
Requirements for a sampling job
| Question | Example answer |
|---|---|
| What is the purpose? | Find how pupils travel to school |
| What is the population? | All 1,200 pupils on the school list |
| How big is the sample? | 120 pupils |
| What must it reflect? | Every year group |
The cells students fill in are left blank in this preview.
Prepare the dataset for sampling
List the whole population, once each. Remove blank and repeated rows. Give every item a unique id.
If an item is listed twice, it gets twice the chance of being picked. That is a bias you caused.
Check
Have a go
Check
3 questionsYour answers are marked here and are not kept. A college account keeps every student’s marks.