Statistics

Read data, compare distributions and examine samples.

Try a practice

Statistics

Data interpretation

Read tables and charts, then compare values, find means or calculate percentages.

6 questions · 3 levels · No time limit

Statistics

Distributions

Reason about averages, medians, spread and outliers. Change a data value to see which conclusions still hold.

1 question · 3 levels · Untimed

Statistics

Sampling

Compare weighted populations and sampling methods. Separate a method’s bias from variation in individual samples.

1 question · 3 levels · Untimed

Statistics

Correlation detective

Uncover a hidden line by removing planted anomalies from a scatterplot.

3 steps · 3 levels · Untimed

Statistics

When averages mislead

Change the group sizes and watch the overall winner change.

3 steps · 3 levels · Untimed

Statistics

Signal or chance?

Shuffle group labels to discover how surprising a difference really is.

3 steps · 3 levels · Untimed

Statistics

Confidence intervals

Draw repeated samples and discover which intervals capture the true mean.

3 steps · 3 levels · Untimed

Statistics

The comeback illusion

Retest unusually high or low scores and separate real change from chance.

3 steps · 3 levels · Untimed

Learn a method

Browse lessons

Lesson

Read data before calculating

Read labels and units, then combine two series to find totals, differences, shares and percentage changes.

6 min · Example and practice

Lesson

Choose a useful center

Compare the mean and median, then explain what an unusually large value changes.

4 min · Example and practice

Lesson

Compare the spread

See why equal means can hide different variability and what standard deviation summarizes.

4 min · Example and practice

Lesson

Question the sample

Distinguish chance differences between random samples from systematic selection bias.

4 min · Example and practice

Lesson

Weight the groups

Combine totals correctly and see how changing group proportions can reverse a comparison.

6 min · Example and practice

Lesson

Inspect the scatter

Investigate influential observations while keeping correlation separate from causation.

4 min · Example and practice

Lesson

Shuffle to test a difference

Use random assignments to understand how surprising a difference is.

5 min · Example and practice

Lesson

Read confidence as coverage

Understand what confidence intervals cover, what more data changes and what bias leaves behind.

6 min · Example and practice

Lesson

Separate change from selection

Distinguish a real effect from the change expected after selecting unusual first results.

6 min · Example and practice