Clinical record review (CRR) scenarios which yielded harm rate estimates with acceptable precision, e.g. estimation errors < ±25% of the real harm rate (rHR). The lines and the zone above and to the right of each line represent those CRR scenarios with acceptable precision. Scenarios vary according to number of practices reviewing records, number of records reviewed per practice and the rHR (indicated by numbers on the lines and measured in incidents/100 patients/year. The median rate ratios (MRR) between patients and practices are 2 and 1.2 respectively. The results are for the beginning of the simulated twelve month period.