Natalia notices that if she does not sleep a lot at night, she feels tired the next day. what relationship (if any) exists between hours of sleep and degree of exhaustion

The answer is that, "There is a negative correlation".

A negative correlation implies that there is a reverse connection between two variables - when one variable reduces, the other increases. The other way around is a negative correlation as well, in which one variable increments and alternate declines. These connections are considered in measurements as a methods for deciding the connection between two factors.

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