Clinician's administration may influence the subject by how they explain the question. Interpretation of the subjects response may also be hindered by the clinician even when methods are present to prevent interviewer biases.
The scale is not intended to be used as a diagnostic instrument.
The MRS follows the style of the Hamilton Rating Scale for depression (Hamilton, 1960) and is intended to be administered, by a trained clinician during a fifteen- to thirty-minute interview. A severity rating is assigned to each of the eleven items, based on the patient's subjective report of his or her condition over the previous forty-eight hours and the clinician's behavioural observations during the interview, with the emphasis on the latter. Four items (5, 6, 8 and 9) are given twice the weight of the remaining seven in order to compensate for poor cooperation from severely ill patients.
Guide for Scoring Items - The purpose of each item is to rate the severity of that abnormality in the patient. When several keys are given for a particular grade of severity, the presence of only one is required to qualify for that rating.
The keys provided are guides. One can ignore the keys if that is necessary to indicate severity, although this should be the exception rather than the rule.
Scoring between the points given (whole or half points) is possible and encouraged after experience with the scale is acquired. This is particularly useful when severity of a particular item in a patient does not follow the progression indicated by the keys.