The answer is DISTINCTCOUNT(SurveyResponses[RespondentID]). This measure works because DISTINCTCOUNT returns the number of unique values in a column, and when placed in a filter context—such as a visual grouped by QuestionID or a slicer on a specific question—it counts only the distinct RespondentID entries tied to that question, giving you the exact number of unique respondents. On the PL-300 exam, this tests your understanding of row context versus filter context and the difference between counting rows (COUNTROWS) and counting distinct entities. A common trap is using COUNT or COUNTROWS, which would count every response row, including duplicates from the same respondent answering multiple questions. To remember: think “unique people, not repeated answers”—DISTINCTCOUNT strips away duplicates, leaving only one count per respondent. A quick mnemonic: “DISTINCTCOUNT gives distinct count—no repeats allowed.”
PL-300 Model the data Practice Question
This PL-300 practice question tests your understanding of model the data. Read the scenario carefully and evaluate each option against the stated constraints before committing to an answer. After answering, compare your reasoning against the explanation and wrong-answer breakdown below. Once you have made your selection, read the full explanation to reinforce the concept and understand why each distractor is designed to mislead on exam day.
You are modeling data in Power BI that includes a table named SurveyResponses with columns: ResponseID, QuestionID, RespondentID, and AnswerText. Each respondent answers multiple questions. You need to create a measure that counts the number of unique respondents who answered a specific question. Which DAX measure should you use?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
DISTINCTCOUNT(SurveyResponses[RespondentID])
Option A is correct because DISTINCTCOUNT(SurveyResponses[RespondentID]) counts the number of unique RespondentID values in the table, which directly gives the count of unique respondents who answered a specific question when used in a filter context (e.g., with a slicer or visual grouping by QuestionID). This is the standard DAX pattern for counting distinct entities in a column.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
✓
DISTINCTCOUNT(SurveyResponses[RespondentID])
Why this is correct
DISTINCTCOUNT returns the count of unique values in the column.
Related concept
Read the scenario before looking for a memorised answer.
✗
COUNT(SurveyResponses[RespondentID])
Why it's wrong here
COUNT counts numbers, but RespondentID is likely text; also it does not count unique.
✗
COUNTROWS(SurveyResponses)
Why it's wrong here
COUNTROWS counts all rows, including multiple responses from the same respondent.
✗
COUNTA(SurveyResponses[RespondentID])
Why it's wrong here
COUNTA counts non-blank values, not unique.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often confuse COUNTROWS (which counts all rows) with DISTINCTCOUNT (which counts unique values), or they assume COUNT or COUNTA will automatically deduplicate, leading them to pick a wrong option that counts total responses instead of unique respondents.
Detailed technical explanation
How to think about this question
Under the hood, DISTINCTCOUNT uses the storage engine to create a distinct list of values from the column and then counts them, leveraging the VertiPaq engine's compression and indexing for efficiency. A subtle behavior is that DISTINCTCOUNT includes blank values as a distinct value if present, so ensure RespondentID has no blanks to avoid overcounting. In a real-world scenario, if a respondent answers the same question multiple times, DISTINCTCOUNT ensures they are counted only once, which is critical for accurate survey analysis.
KKey Concepts to Remember
Read the scenario before looking for a memorised answer.
Find the constraint that changes the correct option.
Eliminate answers that are true in general but not in this case.
TExam Day Tips
→Watch for words such as best, first, most likely and least administrative effort.
→Review why wrong options are wrong, not only why the correct option is correct.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
How this comes up in practice
A cloud solutions architect for a retail company is evaluating services for a new workload. The correct answer here reflects best practice for the specific scenario described — not a general cloud recommendation. Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option. Cloud exam questions reward reading the constraint carefully: the same technology can be right or wrong depending on the use case.
What to study next
Got this wrong? Here's your next step.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Model the data — This question tests Model the data — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: DISTINCTCOUNT(SurveyResponses[RespondentID]) — Option A is correct because DISTINCTCOUNT(SurveyResponses[RespondentID]) counts the number of unique RespondentID values in the table, which directly gives the count of unique respondents who answered a specific question when used in a filter context (e.g., with a slicer or visual grouping by QuestionID). This is the standard DAX pattern for counting distinct entities in a column.
What should I do if I get this PL-300 question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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Question Discussion
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