DA0-002 Data Acquisition and Preparation Practice Question
A data analyst needs to perform a stratified random sample of a customer database. Which TWO steps are essential for this sampling method? (Select two.)
⚠ Common exam trap
The trap is confusing stratified sampling with cluster or systematic sampling — candidates see 'random selection' in multiple options and pick the wrong method because they miss that stratification requires both dividing into strata AND proportional selection within each.
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
✓
Randomly select a proportional number from each stratum
Option D is correct because stratified random sampling begins by partitioning the population into homogeneous subgroups called strata, typically based on a shared characteristic such as age, region, or customer tier, so that each subgroup is internally similar. Option C is correct because, after the strata are formed, the analyst must draw a random sample from each stratum, usually in a number proportional to that stratum's size in the population, ensuring the sample reflects the population's structure. Option A is incorrect because simple random sampling on the whole population ignores the strata and is a different sampling method. Option B is incorrect because randomly selecting entire clusters describes cluster sampling, not stratified sampling. Option E is incorrect because selecting every nth customer is systematic sampling, which does not require dividing the population into strata.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Use simple random sampling on the whole population
Why it's wrong here
Simple random sampling draws from the entire population with equal probability, so no subgroups are formed and proportional representation is not enforced. It is tempting because it is the baseline probability method, but stratified sampling requires first dividing the population into strata, then sampling randomly within each one.
- ✗
Randomly select entire clusters of customers
Why it's wrong here
Cluster sampling randomly selects whole groups and then samples every member within them, so strata are never defined or sampled proportionally. It is tempting because both methods partition a population into groups, but clustering serves convenience and cost reduction, whereas stratification requires splitting by a shared characteristic before random selection within each stratum.
- ✓
Randomly select a proportional number from each stratum
Why this is correct
After dividing the population into strata, drawing a random sample from each stratum in proportion to its size preserves the population's composition. This proportional random selection is what makes the sample stratified rather than a simple random sample.
- ✓
Divide the population into homogeneous subgroups (strata)
Why this is correct
Stratified sampling requires the population be partitioned into homogeneous strata before drawing random samples from each. Dividing into subgroups is the defining structural step; without it, selection would be simple random rather than stratified, so this satisfies the method's core constraint.
- ✗
Select every nth customer from a list
Why it's wrong here
Systematic sampling picks every nth record from one ordered list, which produces a single sample rather than independent random draws inside defined strata. It is tempting because it is a probability method that is quick to apply, yet it cannot guarantee proportional representation of each subgroup the way stratified sampling demands.
Go deeper
Related to this question
About these practice questions
One of 1,004 original DA0-002 practice questions on Courseiva, each with a full explanation and wrong-answer analysis — not exam dumps or protected exam content. Learn why practice questions differ from exam dumps →
JA
Written and reviewed by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
Last reviewed September 2026 · checked against the official CompTIA exam blueprint
This DA0-002 practice question is part of Courseiva's free CompTIA 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 DA0-002 exam.