Do young children always say yes to yes-no questions? A metadevelopmental study of the affirmation bias.

The present study investigated whether yes-no questions would lead to a yes bias in young children. Four experiments were conducted in which 2- to 5-year-olds were asked comprehensible and incomprehensible yes-no questions concerning familiar and unfamiliar objects. Consistent findings were obtained: (a) 2-year-olds displayed a consistent yes bias; (b) 4- and 5-year-olds exhibited no response bias toward comprehensible questions and a nay-saying bias toward incomprehensible questions; and (c) 3-year-olds' results were mixed, suggesting that the age of 3 years is a period of developmental transition in response tendency toward yes-no questions. The findings suggest that yes-no questions are suitable for older children, providing they are comprehensible, but may result in biased results when used with younger children and when incomprehensible.