DA0-002 Data Acquisition and Preparation Practice Question
During exploratory data analysis, you calculate the IQR for a numeric column and find that several data points fall below Q1 - 1.5*IQR. These points are likely:
⚠ Common exam trap
It's easy for candidates to confuse the IQR outlier rule with measures of central tendency — candidates may pick 'mode' or 'median' because those are familiar summary statistics, but the 1.5×IQR fence is specifically the outlier detection rule.
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
✓
Outliers
The 1.5×IQR rule is the standard Tukey fence for identifying outliers in exploratory data analysis. Any value below Q1 − 1.5×IQR (or above Q3 + 1.5×IQR) is flagged as a potential outlier. Since the question states points fall below Q1 − 1.5×IQR, they are by definition outliers.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Normal variations within the distribution
Why it's wrong here
Points below Q1 − 1.5×IQR fall outside the Tukey fence, so they are flagged as potential outliers, not normal variation. The temptation is that some spread around the quartiles is expected, but the fence is deliberately set beyond typical variation; only points inside the fences qualify as normal.
- ✗
The mode of the dataset
Why it's wrong here
The mode is the most frequent value, a measure of central tendency, and cannot be identified by falling below Q1 − 1.5×IQR. The temptation is to associate any notable group of points with a summary statistic, but the IQR fence flags outliers; the mode would be the correct choice when asked for the most common value.
- ✗
The median of the dataset
Why it's wrong here
The median is the middle value (Q2), which always sits inside the IQR, so it cannot lie below Q1 − 1.5×IQR. The temptation is to treat any labelled point as a central measure, but the fence identifies outliers; the median would be the correct choice when asked for the dataset's central value.
- ✓
Outliers
Why this is correct
Values below Q1 - 1.5*IQR sit outside Tukey's fence, the standard IQR rule for flagging extreme observations. Since the stem specifies this exact threshold, those points are classified as outliers, though they may still be legitimate values requiring investigation rather than automatic removal.
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Senior Network & Security Engineer · founder of Courseiva
Last reviewed September 2026 · checked against the official CompTIA exam blueprint
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