Final answer:
The order in which the participants experience different sleep durations affects their test scores is an example of an order effect. The correct answer is d) The order in which the participants experience different sleep durations affects their test scores.
Step-by-step explanation:
An order effect in a repeated-measures study refers to changes in participants' scores that are the result of the order in which different conditions are experienced, rather than the conditions themselves.
This is particularly important in studies measuring the effects of variables such as sleep on performance. This implies that the scores might be influenced by whether the participant had more or less sleep first, which could affect their subsequent performance on the mathematics test.
In a repeated-measures study, like the one described in the question, participants would act as their own control by taking the test under different conditions of sleep duration.
Random assignment of the order in which participants receive different levels of sleep can help mitigate order effects, as each participant has an equal chance of experiencing the conditions in any given order.
A repeated-measures design was also evident in the study where subjects were tested on their mean hours of sleep before and after starting a new medication, ensuring that each subject experienced both 'treatments'—with and without the medicine.
In the context of the provided question, the correct answer is (d) The order in which the participants experience different sleep durations affects their test scores.