# Table 2 The precision\$of selected clinical record review (CRR) scenarios’ estimated harm rates

Practices (n) Records reviewed per practice (n) Estimation error (%)\$
rHR* = 2 rHR* = 5 rHR* = 10 rHR* = 20
1 20 - - - -
25 - - - -
50 - - - -
100 - - - 107
150 - - 132 88
200 - - 107 74
10 20 - - 107 74
25 - 146 96 67
50 - 96 65 46
100 107 65 46 32
150 88 54 37 26
200 74 46 32 23**
20 20 - 107 74 51
25 - 96 65 46
50 107 65 46 32
100 74 46 32 23
150 60 37 26 18
200 51 32 23 16
50 20 107 67 46 32
25 96 58 41 29
50 65 41 29 20
100 46 29 20 14
150 37 23 17 12
200 32 20 14 10
100 20 74 46 32 23
25 65 41 29 20
50 46 29 20 14
100 32 20 14 10
150 26 17 12 8
200 23 14 10 7
150 20 60 37 26 18
25 54 33 23 17
50 37 23 16 12
100 26 17 12 8
150 21 13 10 7
200 18 12 8 6
200 20 52 32 23 16
25 46 29 20 14
50 32 20 14 10
100 23 14 10 7
150 18 12 8 6
200 16 10 7 5
250 20 46 29 20 14
25 41 26 18 13
50 29 18 13 9
100 20 13 9 6
150 17 10 7 5
200 14 9 6 5
300 20 42 26 18 13
25 37 23 17 12
50 26 17 12 8
100 18 12 8 6
150 15 10 7 5
200 13 8 6 4
1. \$Precision is expressed as percentage estimation error, averaged across 1000 simulated studies for each CRR scenario.
2. *rHR (real harm rate): The actual, underlying ‘baseline’ harm rate, expressed as number of incidents/100 patients/year. The harm rates estimated by different CRR scenarios are not shown.
3. **Example: In this CRR scenario, 10 practices each reviewed 200 records and the estimation error was ±23%, e.g. within ±23% of the rHR of 20 incidents/100patients/year. The estimation error (%) indicates the proximity between the harm rate estimated by that unique CRR scenario and the rHR. Smaller estimation errors therefore indicate greater precision. We defined acceptable precision as estimation errors < ±25%.
4. Scenarios vary by numbers of practices reviewing records, number of records reviewed in each practice and real harm rates (rHR)*. The median rate ratios (MRR) between patients and practices are 2 and 1.2 respectively. The results are from the beginning of the simulated 12-month period.