Professor Izadi is interested in the association between sleep and cognitive performance. He surveyed his students about the number of hours they slept the night before the exam and then correlated these scores with their test grades. He found a +.81 correlation between these two variables. What does this result mean?

There is a high positive correlation between sleep and exam performance.

Explanation:+81 is a high positive correlation which means there is a high degree of relationships between these two variables such that when hours of sleeping increases dramatically so does the cognitive performance increases dramatically. This doesn't explain the cause because correlation doesn't mean causation but it still tells us that they are highly related to each other , positively.