The answer is that the median remains unchanged. This is because median imputation replaces only the missing values with the median value of 52000, and since the median is a positional statistic, adding new entries equal to the current median does not shift the middle of the sorted dataset. The original non-missing values stay exactly as they were, so the central position—and thus the median—stays the same. On the CompTIA Data+ DA0-001 exam, this question tests your understanding that imputation with a central measure like the median preserves that measure’s value, a common trap being to assume any imputation changes the statistic. A useful memory tip: "Median in, median out—adding the middle keeps the middle."
DA0-001 Analyzing and Modeling Data Practice Question
This DA0-001 practice question tests your understanding of analyzing and modeling 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.
Exhibit
Refer to the exhibit.
Python pandas code and output:
```
import pandas as pd
df = pd.read_csv('employees.csv')
df['salary'].fillna(df['salary'].median(), inplace=True)
print(df['salary'].describe())
```
Output:
```
count 1000.000000
mean 55000.000000
std 15000.000000
min 25000.000000
25% 45000.000000
50% 52000.000000
75% 65000.000000
max 120000.000000
Name: salary, dtype: float64
```
Refer to the exhibit. Before running the code, the original salary column had 50 missing values. The median was calculated as 52000. After imputation, which of the following statements is true?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The median remains unchanged
Imputing missing values with the median (52000) replaces only the 50 missing entries with that value, leaving all original non-missing values unchanged. Since the median is a positional statistic, adding values equal to the current median does not shift the middle position of the sorted data, so the median remains unchanged. This is why option C is correct.
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.
✗
The mean decreased significantly
Why it's wrong here
Imputing median may shift the mean slightly, but not significantly, especially if only 5% are missing.
✗
The standard deviation increased
Why it's wrong here
Imputing with median typically reduces variance, so standard deviation may decrease.
✓
The median remains unchanged
Why this is correct
Since missing values are replaced by the median, the median of the dataset does not change.
Related concept
Read the scenario before looking for a memorised answer.
✗
The minimum value decreased
Why it's wrong here
The minimum value is from an original non-missing value and is unaffected by imputation.
Common exam traps
Common exam trap: answer the scenario, not the keyword
CompTIA often tests the misconception that imputing with the median will change the median itself, when in fact adding values equal to the current median leaves the median unchanged because it is a rank-based statistic.
Detailed technical explanation
How to think about this question
Median imputation is a robust technique that preserves the central tendency without being influenced by outliers, but it artificially reduces variability by compressing the distribution toward the median. In practice, this can lead to underestimated standard errors and inflated Type I error rates in subsequent hypothesis tests. A subtle behavior: if the missing data are not missing completely at random (MCAR), median imputation can introduce bias in the mean and distort relationships with other variables.
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 practitioner preparing for the DA0-001 exam encounters this exact type of scenario on the job. The correct answer here is not the most general option — it is the best answer for the specific constraint described. Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option. Real exam questions reward reading the full scenario before eliminating options, because the constraint defines which answer fits.
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.
Analyzing and Modeling Data — This question tests Analyzing and Modeling Data — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: The median remains unchanged — Imputing missing values with the median (52000) replaces only the 50 missing entries with that value, leaving all original non-missing values unchanged. Since the median is a positional statistic, adding values equal to the current median does not shift the middle position of the sorted data, so the median remains unchanged. This is why option C is correct.
What should I do if I get this DA0-001 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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