[Methodological constraints in evaluating anti-deficit effects]

Several types of limitations are inherent in the evaluation of changes in negative symptoms during clinical trials. Some of these limitations can be listed as follows: the need to select homogeneous study populations (use of a standardized diagnosis), identification of negative dimensions which feature deficitary forms of schizophrenia (qualitative criteria and threshold scores using negative symptom rating tables), strict control of variables which may induce secondary negative symptoms (treatments, other associated disorders particularly of a depressive type, lack of environmental stimulus), follow-up of stability of negative symptoms and, finally, an adequate time interval for evaluation in order to exclude spontaneous and non-specific fluctuations of symptomatology.