Events that occur between the first and second measurement period but are not part of the manipulation are called _____ effects.

A) history
B) maturation
C) testing
D) cohort

History effects refer to external events that occur between the first and second measurement period but are not part of the manipulation. Maturation refers to changes within the participants themselves, such as physical or emotional growth, that occur naturally over time. Testing effects refer to the impact of simply taking the first measurement on subsequent responses. Cohort effects refer to differences in responses that are tied to characteristics of the participants' generation (e.g., millennials vs. baby boomers).