  In national research assessment exercises that take the peer review approach,
research organizations are evaluated on the basis of a subset of their
scientific production. The dimension of the subset varies from nation to nation
but is typically set as a proportional function of the number of researchers
employed at each research organization. However, scientific fertility varies
from discipline to discipline, meaning that the representativeness of such a
subset also varies according to discipline. The rankings resulting from the
assessments could be quite sensitive to the size of the share of articles
selected for evaluation. The current work examines this issue, developing
empirical evidence of variations in ranking due changes in the dimension of the
subset of products evaluated. The field of observation is represented by the
scientific production from the hard sciences of the entire Italian university
system, from 2001 to 2003.

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