During the first year of life, the trunk grows the fastest. During the second year of life, the legs grow the fastest. Which principle does this illustrate?

Assignment bias is a threat to external validity

a. True b. False Indicate whether the statement is true or false

Marlene likes to get email, and she checks her electronic mailbox frequently. Sometimes she gets 15 messages in a single day, and sometimes several days can go by with no new messages coming in. Based on what is known about schedules of reinforcement, you should conclude that Marlene's behavior of "checking her email" is being reinforced based on a:

a. fixed-ratio schedule b. variable-ratio schedule c. variable-interval schedule d. fixed-interval schedule