MLS-C01 Exploratory Data Analysis Practice Question
A team is performing exploratory data analysis on a dataset containing 10 million records stored in Amazon S3. They want to sample the data efficiently to build a representative subset for initial modeling. Which sampling method should they use to minimize bias and ensure the sample reflects the population distribution?
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
✓
Stratified random sampling
(Stratified random sampling) is correct because it divides the dataset into homogeneous subgroups (strata) and samples proportionally from each, ensuring all subgroups are represented and reducing bias. This is especially important when the data is imbalanced. Option B (Simple random sampling) is incorrect because it may underrepresent or miss rare subgroups, leading to biased samples. Option C (Systematic sampling) is incorrect because it can introduce bias if the data has periodic patterns. Option D (Reservoir sampling) is incorrect because it is designed for streaming data where the total size is unknown, not for a static dataset of 10 million records in Amazon S3.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
Stratified random sampling
Why this is correct
Stratified sampling ensures representation from all strata, reducing bias.
- ✗
Simple random sampling
Why it's wrong here
Simple random sampling may not represent small subgroups well.
- ✗
Systematic sampling
Why it's wrong here
Systematic sampling can be biased if the data has patterns.
- ✗
Reservoir sampling
Why it's wrong here
Reservoir sampling is used for streaming data, not for static datasets.
Quick reference
AWS S3 Storage Class Comparison
| Storage Class | Min Duration | Retrieval | Use Case |
|---|---|---|---|
| S3 Standard | None | Immediate | Frequently accessed data |
| S3 Standard-IA | 30 days | Immediate | Infrequent access, rapid retrieval |
| S3 One Zone-IA | 30 days | Immediate | Non-critical infrequent data |
| S3 Intelligent-Tiering | None | Immediate–hours | Unknown or changing access patterns |
| S3 Glacier Instant | 90 days | Milliseconds | Archive with instant retrieval |
| S3 Glacier Flexible | 90 days | Minutes–hours | Archive, flexible retrieval |
| S3 Glacier Deep Archive | 180 days | Hours | Long-term compliance archive |
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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.