High Train/Val/Test Question 151 of 223

Why must medical or user data be split by patient or user, not by row?

AI & Data Analytics · Speak this in 60–90 seconds · Faridabad & Delhi NCR

PICTURE THIS: DATA SPLIT

Train 70%Val 15%Test 15%

Fit on train, tune on val, report on test once.

Simple meaning

Multiple rows from one person share physiology, devices, and labeling quirks.

WHY — Train/Val/Test instead of guessing?

Why interviewers care about Train/Val/Test:

They are checking judgment

on Train/Val/Test.

A good answer names

the situation, the default choice, and one exception - that reads as experience.

Stay structured

Name the idea, why it exists, then one short example.

Close cleanly

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:

1
Multiple rows from one
person share physiology, devices, and labeling quirks.
2
A row-wise split puts
the same person in train and test, so scores look like generalization when they are memorization.
3
Grouped splits and GroupKFold
are the honest design.
4
Give an example
One tiny concrete case you can say aloud.
5
Common mistake
What juniors usually get wrong.
6
Close
When you pick this over the alternative.

EXAMPLE — See it in action

Here's a short line you can speak, broken into clear beats:

Say this line

“A row-wise split puts the same person in train and test, so scores look like gen”

Break into beats

Arowwisesplitputsthe

Speaking order

2987408337471632900

Note: Adapt this scaffold to your own project — keep it under 60–90 seconds.

Key takeaway

Multiple rows from one person share physiology, devices, and labeling quirks. A row-wise split puts the same person in train and test, so scores look like generalization when they are memorization.