  With the passage of more time from the original date of publication, the
measure of the impact of scientific works using subsequent citation counts
becomes more accurate. However the measurement of individual and organizational
research productivity should ideally refer to a period with closing date just
prior to the evaluation exercise. Therefore it is necessary to compromise
between accuracy and timeliness. This work attempts to provide an order of
magnitude for the error in measurement that occurs with decreasing the time
lapse between date of publication and citation count. The analysis is conducted
by scientific discipline on the basis of publications indexed in the Thomson
Reuters Italian National Citation Report.
