___________ effects are seen when the results of a study might not be able to be generalised simply because of how long the longitundinal design took to run

A researcher is worried that changes in the early education curriculum might account for the age-related differences in socio-emotional skills that she is seeing in her study of 4-year-olds, 6-year-olds and 8-year olds. She is worried about a _______ effect.

1. ___________effects are seen when participants of different ages might differ in how they perform on a test, because of some other variable, other than age.