A survey about school meals only asks students in one class. Name one issue.

Answer: Sampling bias; sample may not represent the whole school.

Two variables are strongly correlated. Can we conclude causation?

Answer: No, correlation alone is insufficient.

A bar chart axis starts at 95 instead of 0. Why can this mislead?

Answer: Differences look much larger than they really are.

“Risk increased from 1% to 2%.” State absolute and relative increase.

Answer: Absolute +1 percentage point; relative increase 100% (doubled).

Name one way to improve reliability of a poll.

Answer: Use a larger random sample from the target population.

Checkpoints