Author note — to cover

Identify bias from the time, place and method of selection and from self-selection, in described surveys such as lunchtime polls outside a gym. Question type: name the excluded group and the direction results skew. No numerical corrections or weighting. Sample size is the sibling page; question wording is on Questionnaires. Both tiers. (S1)

• Fluency — direct questions on bias in sampling, limited to this lesson's stated scope (4 questions).
• Application — use the same skill in unfamiliar or contextual questions without introducing a later method (4 questions).
• Check — questions built around the exclusions and likely misconceptions named in the lesson brief (4 questions).