Question 386 of 1,672
MLS-C01 Modeling Practice Question
A data scientist is using principal component analysis (PCA) for dimensionality reduction before training a classifier. The classifier's performance on the test set is poor. What is the most likely cause?
⚠ Common exam trap
AWS often tests the misconception that PCA always improves classifier performance by removing noise, but the trap here is that candidates may overlook the risk of underfitting when too few components are retained, especially when the discarded variance contains critical discriminative features.
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Too few principal components were retained, losing important information
C is correct because PCA is an unsupervised dimensionality reduction technique that projects data onto principal components capturing the maximum variance. If too few components are retained, the reduced representation may discard features that are critical for the classifier to distinguish between classes, leading to poor test performance due to underfitting.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
The classifier is overfitting
Why it's wrong here
Test set performance poor indicates overfitting, but it's not directly caused by PCA.
- ✗
The data was not scaled before applying PCA
Why it's wrong here
Scaling affects PCA but not necessarily poor classification.
- ✓
Too few principal components were retained, losing important information
Why this is correct
Discards discriminative features.
- ✗
Too many principal components were retained, including noise
Why it's wrong here
May cause overfitting, but not most likely.
About these practice questions
Courseiva creates original exam-style practice questions with explanations and wrong-answer analysis. It does not publish real exam questions, exam dumps, or protected exam content. Learn why practice questions differ from exam dumps →
Last reviewed: Jun 30, 2026
This MLS-C01 practice question is part of Courseiva's free Amazon Web Services certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the MLS-C01 exam.
Question Discussion
Share a tip, memory trick, or ask about the reasoning behind this question. Do not post real exam questions, leaked content, braindumps, or copyrighted exam material. Comments are moderated and may be removed without notice.
Sign in to join the discussion.