A dentist wants to find out how often her patients floss their teeth. Which samples are biased? Check all that apply.all her patientspatients with no cavitiespatients younger than 18every 20th patientevery patient with braces

A sample is biased if it focuses on a group that may floss differently from all of the dentist’s patients. Patients with no cavities may floss more often, and patients younger than 18 or patients with braces may have different flossing habits from the overall patient group. Asking all her patients includes the whole group, while every 20th patient is a systematic sample that can represent it.

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