a common symptom of *depression, in which the patient regularly experiences different mood states at different times of day. Classically, a depressed patient will complain of particularly low mood in the morning and this gradually improves during the day.
The tendency for the estimated magnitude of a parameter (e.g. based upon the average of a sample of observations of a treatment or intervention effect) to deviate randomly from the true magnitude of that parameter. Random variation is independent of the effects of systematic biases. In general, the larger the sample size, the lower the random variation of the estimate of a parameter. As random variation decreases, precision increases.... random variation / random error
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