What is the difference between MCAR, MAR, and MNAR?
PICTURE THIS: 1, 2, 2, 8
Simple meaning
MCAR means missingness is unrelated to observed and unobserved values.
WHY — Missing Data instead of guessing?
Why interviewers care about Missing Data:
contrast on Missing Data, not two memorised paragraphs.
the developer, then one case where picking wrong hurts.
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:
- 1MCAR means missingness is
unrelated to observed and unobserved values.
- 2MAR means missingness depends
on observed covariates but not on the missing value itself given those covariates.
- 3MNAR means missingness depends
on the unobserved value, such as high spenders hiding income, which needs stronger modeling assumptions.
- 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
MCAR means missingness is unrelated to observed and unobserved values. MAR means missingness depends on observed covariates but not on the missing value itself given those covariates.