What is selection bias in a dataset?
PICTURE THIS: 1, 2, 2, 8
Simple meaning
Selection bias means the sample does not represent the population you care about.
WHY — Bias instead of guessing?
Why interviewers care about Bias:
who only read docs from people who shipped.
and tied to Data Science work.
Name the idea, why it exists, then one short example.
End with when you use it and one common pitfall.
STEPS — What happens step by step?
Before you speak the answer, walk the interviewer through these steps:
- 1Selection bias means the
sample does not represent the population you care about.
- 2Online surveys that only
reach active users are a classic case.
- 3Models then fail on
real traffic.
- 4Give an example
One tiny concrete case you can say aloud.
- 5Common mistake
What juniors usually get wrong.
- 6Close
When you pick this over the alternative.
EXAMPLE — See it in action
Here's a short line you can speak, broken into clear beats:
Note: Adapt this scaffold to your own project — keep it under 60–90 seconds.
Key takeaway
Selection bias means the sample does not represent the population you care about. Online surveys that only reach active users are a classic case.