Ask them, or look it up?
A youth club wants to know which snacks to stock. Zara can make a survey and ask every member. Or she can look at last year's till records.
Both give answers. They are not the same kind of data, and each has strengths and limits.
Key words
| Word | What it means | Example |
|---|---|---|
| Primary data | Data you collect yourself, for your own question. | A survey you write |
| Secondary data | Data that someone collected earlier, for another reason. | Last year's till records |
| Survey | A set of questions asked to many people. | Which snack do you like? |
| Questionnaire | The list of written questions in a survey. | A paper form |
| Informed consent | A person agrees after being told how their data will be used. | A tick box with a clear note |
| Observation | Watching and recording what happens. | Counting visitors at the door |
| Relevance | How well the data fits your question. | Snack choices fit a snack question |
The cells students fill in are left blank in this preview.
By the end of this lesson
Note
I can compare primary and secondary data on six points and say which one a task needs.
Starter: where would you look?
Have a go
Starter: where would you look?
3 questionsYour answers are marked here and are not kept. A college account keeps every student’s marks.
Six differences
| Point | Primary | Secondary |
|---|---|---|
| Purpose | Used for the reason it was collected | Used for a new reason |
| Age | Current | Past |
| Sources | Surveys, observations, questionnaires, interviews | Forums, government publications, internal records |
| Relevance | Made to fit your need | Useful, but not made for you |
| Legitimacy | You need permission and informed consent | Permission may be needed, depending on use |
| Availability | You must plan it: slow and hard work | Ready to use and easy to reach |
The cells students fill in are left blank in this preview.
The trade-off
Primary data fits your question exactly. But it takes time and effort, and you must get consent.
Secondary data is quick and cheap. But it may be old, and it was not made for your question. Good analysts often use both: secondary data to start, primary data to fill the gaps.
Try it: label each find
select name,
case
when origin in ('survey', 'interview', 'observation') then 'primary'
else 'secondary'
end as kind
from finds
order by name;
-- Try it: add 'forum' to the primary list and press Run.A common mistake
Warning
Many people think secondary data is second best. It is not. For a big question about a whole town, a government table is better than any survey you could run. The best data is the data that fits the question.