DAC Data Analysis Fundamentals 2 — Questions and Answers
Question 1: A dataset column stores customer ages but a few entries read 'unknown'. What data quality issue does this represent?
- Missing values (Correct answer)
- Duplicate records
- Outliers
- Data redundancy
Correct answer: Missing values
Non-numeric placeholders like 'unknown' in a numeric field are a form of missing or null data.
Question 2: Which measure of central tendency is LEAST affected by extreme outliers?
- Mean
- Median (Correct answer)
- Range
- Standard deviation
Correct answer: Median
The median depends only on the middle position, so extreme values barely shift it.
Question 3: You need to combine two tables sharing a common customer_id column. Which operation is appropriate?
- Join (Correct answer)
- Pivot
- Filter
- Sort
Correct answer: Join
A join merges rows from two tables based on a shared key column.
Question 4: A chart shows sales rising every December for three years. This repeating pattern is called what?
- Trend
- Seasonality (Correct answer)
- Noise
- Correlation
Correct answer: Seasonality
Seasonality is a pattern that repeats at regular calendar intervals.
Question 5: Which data type best represents a 'yes/no' survey response?
- Continuous
- Boolean (Correct answer)
- Ordinal
- Interval
Correct answer: Boolean
A two-state true/false response is naturally modeled as a Boolean value.
Question 6: In descriptive statistics, what does standard deviation measure?
- The most frequent value
- The spread of values around the mean (Correct answer)
- The middle value
- The total count
Correct answer: The spread of values around the mean
Standard deviation quantifies how far values typically deviate from the mean.
Question 7: A report double-counts revenue because the same order appears twice. What cleaning step fixes this?
- Normalization
- Deduplication (Correct answer)
- Aggregation
- Imputation
Correct answer: Deduplication
Deduplication removes repeated records so each entity is counted once.
DAC Data Analysis Fundamentals 2
A dataset column stores customer ages but a few entries read 'unknown'.
What data quality issue does this represent?