Question 1,125 of 1,672
MLS-C01 Exploratory Data Analysis Practice Question
A data analyst is performing exploratory data analysis on a dataset and notices that there are outliers in several numerical columns. Which TWO methods can the analyst use to identify outliers?
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
✓
Calculate z-scores and flag any data points with |z| > 3.
Options B and C are correct. Box plots use the IQR to identify outliers as points outside 1.5*IQR from the quartiles (option C). Z-scores identify outliers as points with |z| > 3, assuming a roughly normal distribution (option B). Option A (scatter plot matrix) can help visualize outliers but is not a systematic detection method. Option D (comparing mean and median) provides insight into skewness but does not directly flag outliers. Option E (histogram) shows distribution shape but requires subjective judgment to identify 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.
- ✗
Create a scatter plot matrix to visually inspect.
Why it's wrong here
Creating a scatter plot matrix can help visually inspect for outliers but is not a systematic detection method.
- ✓
Calculate z-scores and flag any data points with |z| > 3.
Why this is correct
Calculating z-scores and flagging points with |z| > 3 is a standard statistical method for outlier detection, assuming the data is roughly normally distributed.
- ✓
Use a box plot to visualize the interquartile range (IQR) and identify points outside the whiskers.
Why this is correct
Using a box plot to visualize the IQR and identifying points outside the whiskers (1.5*IQR) is a common and effective method for outlier detection.
- ✗
Compare the mean and median of each column.
Why it's wrong here
Comparing the mean and median of each column can indicate skewness but does not directly identify outliers.
- ✗
Plot a histogram and look for gaps.
Why it's wrong here
Plotting a histogram shows the distribution shape but requires subjective judgment to identify outliers; it is not a systematic method.
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Last reviewed: Jun 20, 2026
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