Table 1

Predictions of error rates obtained by reliability modelling. Results were multiplied by 1000 to define rates per 1000 cases

ProcessPotential adverse events/1000 casesUnmitigated potential adverse events/1000 cases (95% recall rate)Unmitigated potential adverse events/1000 cases (99% recall rate)
Radiologist interprets radiograph3(a)3(a)3(a)
Before initial improvements:
40% of cases interpreted by radiologists; 60% of cases interpreted by emergency physician with radiologist doing subsequent reading19(b)2.2(c)1.4
After initial improvements:
40% of cases interpreted by radiologists; 60% of cases interpreted by emergency physician with radiologist doing subsequent reading8.4(d)1.6(e)1.3
Redesigned system:
Emergency physician interprets all radiographs; radiologist does subsequent reading3(f)0.16(g)0.039
  • (a) See assumption 2. The rate of potential adverse events and the rate of adverse events are the same since there is no subsequent reading by a radiologist.

  • (b) The weighted average of the error rates of 0.03 for emergency physicians and 0.003 for radiologists (assumption 4).

  • (c) The sum of three components: 0.4(0.003) + 0.6(0.03)(0.003) + 0.6(0.03)(0.997)(0.05). The first is the contribution of an error by the radiologist. The second is the contribution of an error by the emergency physician that is not identified on the subsequent reading. The third is the case in which an error made by the emergency physician is identified by the radiologist but the patient does not return for appropriate care (assumption 6).

  • (d) Same as (b) with the improved error rate of 0.012 for the emergency physician substituted for the initial rate of 0.03.

  • (e) Same as (c) with the exception of the new error rate of 0.012.

  • (f) Error rate for emergency physicians after the system was redesigned.

  • (g) Sum of two components: the first, (0.003)(0.003), represents an error by the emergency physician that is undetected by the radiologist. The second, (0.003)(0.997)(0.05), represents the case in which an error by the emergency physician is identified by the radiologist but the patient does not return for appropriate treatment.