Table 1.

Number and incidence of adverse events and preventable adverse events among patients discharged from hospitals in Utah and Colorado in 1992 by age group

	Patients aged 16-64 years				Patients aged ⩾65 years			Difference in incidence (P value)
	Unweighted No of events*	Weighted events†			Unweighted No of events*	Weighted events†
		No of events	Incidence (% (SE))			No of events	Incidence (% (SE))
All adverse events	241	8901	2.80 (0.18)		207	7419	5.29 (0.37)	0.001
Preventable adverse events	132	5038	1.58 (0.14)		117	4134	2.95 (0.28)	0.001

^*No of events noted in random sample of 15 000 patient records. 

^†Extrapolation of unweighted results to represent all hospital discharges in Utah and Colorado in 1992.