DA0-002 Data Concepts and Environments Practice Question
An analyst is profiling a table of laboratory test results. The ResultValue column stores numeric readings, but a subset of rows contains the literal text "N/A" in that column, and a separate ResultUnit column records units such as mg/dL or mmol/L. The analyst must compare average ResultValue across two hospital sites. Which data issue most directly prevents a valid comparison, and what is the appropriate first step?
⚠ Common exam trap
The trap here is assuming an average still works on a column that contains text, when the presence of a non-numeric value can change the column's type and silently corrupt the aggregation.
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
✓
The "N/A" text forces the column to be interpreted as text, so numeric averages silently ignore or misorder values, and the analyst must convert or exclude those values before averaging
A numeric column polluted with text values like "N/A" typically gets coerced to a string type, which breaks arithmetic aggregation and can cause silent misordering or failed averages. The analyst must first isolate the non-numeric rows and convert or exclude them so the column is genuinely numeric, then compute the average for each site. Only after that remediation does the two-site comparison become valid.
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 average must be computed as a median because laboratory results are always skewed, so the analyst should replace ResultValue with a rank-based statistic
Why it's wrong here
Skewness can justify using a median, but nothing in the scenario establishes that the distribution is skewed enough to invalidate a mean. The concrete, described defect is the presence of text in a numeric field, which undermines the type of the column before any statistic is chosen. Switching statistics would not repair the underlying type problem.
- ✗
The presence of "N/A" text in a numeric column makes the column string-typed, so the analyst must drop the entire ResultValue column before comparing sites
Why it's wrong here
Detecting non-numeric text indicates a data quality problem, but dropping the whole column discards valid numeric readings along with the unusable ones. The analyst can instead isolate the offending rows and decide how to treat them. Removing the column entirely would also eliminate the measure the comparison depends on, making the analysis impossible rather than cleaner.
- ✗
The ResultUnit column contains multiple unit systems, so the analyst must convert all readings to a single unit before averaging
Why it's wrong here
Mixed units are a real concern for any cross-site comparison, but in this scenario the unit column is present and the described blocker is the literal "N/A" text inside the numeric column. Unit conversion would still be required after fixing that type problem, yet it is not the issue that directly prevents the average from computing correctly. The question asks for the most direct blocker.
- ✓
The "N/A" text forces the column to be interpreted as text, so numeric averages silently ignore or misorder values, and the analyst must convert or exclude those values before averaging
Why this is correct
When a numeric column contains text sentinels, many tools coerce the whole column to a string type, so AVG either fails or sorts lexicographically, producing meaningless results. The analyst must identify the non-numeric rows, decide whether to convert them to nulls or exclude them, and then compute the average on a clean numeric type. Only then is the two-site comparison trustworthy.
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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
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