Statistics & Visualization Mock Test
Consolidate Sessions 25–29 — descriptive stats, probability, correlation, chart selection, and DAX — in one timed mock test.
How to Take This Mock Test
- Attempt the self-test questions below without peeking — answer out loud.
- Then take the 10-question graded quiz at the bottom.
- Aim for 8/10 or better. Anything you miss, review that session.
Part A — Statistics (Self-Test)
A1. Which is more robust to outliers — mean or median?
Median — it only depends on the middle position, not extreme values.
A2. What does standard deviation measure?
The spread of data around the mean, in the same units as the data.
A3. What's the empirical rule for a normal distribution?
68% within 1 SD, 95% within 2 SD, 99.7% within 3 SD of the mean.
A4. What is the Central Limit Theorem?
As sample size grows, the distribution of the sample mean approaches normal, regardless of the population shape.
A5. Does a correlation of 0.9 prove causation?
No — correlation ≠ causation. A confounding variable may drive both.
A6. In sales = 2.5 × ad_spend + 1000, what is the slope?
2.5 — each unit of ad spend is associated with 2.5 more sales.
Part B — Visualization & Dashboards (Self-Test)
B1. Which chart shows a trend over time?
A line chart.
B2. What's the difference between a bar chart and a histogram?
Bar = compare categories; histogram = distribution of one numeric variable.
B3. What's the difference between a measure and a calculated column in DAX?
A measure is computed dynamically (not stored); a calculated column is stored per row.
B4. Which Power BI component cleans and transforms data?
Power Query.
B5. What should you establish first before building a dashboard?
Its purpose and audience.
Interview Questions — Top Statistics & Visualization Picks
The highest-frequency statistics/viz questions. Self-test before revealing.
IQ1. What's the difference between mean and median, and when do you use each?
Model answer: "Mean is the average, median the middle value. I use mean for symmetric data and median when data is skewed or has outliers, since the median is robust."
IQ2. Explain the Central Limit Theorem and why it matters.
Model answer: "As sample size grows, the distribution of the sample mean approaches normal regardless of the population shape — which is why normal-based methods work on sample means."
IQ3. What's the difference between correlation and causation?
Model answer: "Correlation means two variables move together; causation means one drives the other. Correlation doesn't prove causation — a confounder may drive both."
IQ4. How do you interpret R-squared?
Model answer: "R² is the proportion of variance in the outcome explained by the model, from 0 to 1. An R² of 0.9 means the model explains 90% of the variation."
IQ5. What makes a data visualization effective?
Model answer: "It answers one clear question, uses the right chart, is clean and labeled, and communicates the insight without forcing the viewer to work. Good visualization reduces cognitive load."
IQ6. What's the difference between a measure and a calculated column in Power BI?
Model answer: "A measure is computed dynamically at query time and not stored; a calculated column is stored for each row at refresh. I use measures for aggregations, columns for row-level values."
IQ7. What is a KPI, and how do you choose which KPIs to show?
Model answer: "A KPI is a metric tied to a business goal. I choose KPIs after understanding the decision the dashboard supports — the metrics that best track that goal."
IQ8. How would you explain a p-value in plain English?
Model answer: "A p-value is the probability of seeing a result as extreme as the one observed, assuming there's no real effect. A small p-value suggests the result probably isn't just noise."
Key Takeaways
Median is robust to outliers; mean is not.
Correlation ≠ causation; the CLT makes normal methods usable.
Match chart to question; define purpose before building a dashboard.
Measure = dynamic; calculated column = stored; Power Query cleans.
You've completed Phase 4 — ready for the mock rounds ahead.
Objective Questions — The Graded Mock Test (10 Questions)
Q1. Which measure of central tendency is most affected by outliers?
Q2. The Pearson correlation coefficient ranges from…
Q3. In a normal distribution, ~68% of data falls within…
Q4. "Correlation does not imply ___"
Q5. What does R-squared (R²) measure?
Q6. Which chart is best for showing a trend over time?
Q7. What is DAX?
Q8. What's the key difference between a measure and a calculated column?
Q9. Which Power BI component cleans and transforms data?
Q10. What does KPI stand for?