| Reporting period | n (%) |
| Non-intensive | 370 (63) |
| Intensive* | 204 (35) |
| Don’t know | 16 (3) |
| No. of errors per event report | |
| 1 | 302 (51) |
| 2 | 208 (36) |
| 3 | 72 (12) |
| 4 | 8 (1) |
| Error cascades† | |
| Single error | 302 (51) |
| More than one error | |
| Independent errors | 29 (5) |
| Cascade of errors | 231 (39) |
| Cascade and independent errors | 28 (5) |
| Place of occurrence | |
| Offsite | 117 (20) |
| Onsite | 360 (61) |
| Both | 79 (13) |
| Unknown | 34 (6) |
| Specific location of the error(s)‡ | |
| Reporter’s office | 412 (60) |
| Nursing home | 6 (1) |
| Hospital | 39 (6) |
| Emergency department | 4 (1) |
| Onsite lab | 54 (8) |
| Offsite lab | 126 (18) |
| Radiology | 30 (4) |
| Other site (eg, home, other office) | 11 (2) |
| Estimated frequency of occurrence in this practice | |
| This is the first time it has occurred | 60 (10) |
| Seldom (once or twice per year) | 111 (19) |
| Sometimes (three to 11 times per year) | 209 (35) |
| Frequently (more than once per month) | 204 (35) |
| Not reported | 6 (1) |
| Seriousness | |
| Not very serious | 97 (16) |
| Somewhat serious | 216 (37) |
| Serious | 143 (24) |
| Very serious | 89 (15) |
| Extremely serious | 39 (7) |
| Not reported | 6 (1) |
| Actions taken as a result of the error‡ | |
| No intervention/activity specific to event | 71 (12) |
| Medical attention or intervention | 117 (19) |
| Other intervention | 298 (48) |
| Unable to determine | 121 (20) |
| System, protocol, or practice change | 8 (1) |
*During intensive reporting periods, participants were instructed to report every error in the testing process that they observed. Intensive reporting occurred for four of the 32 reporting weeks for each practice at staggered intervals.
†An error “cascade” was noted if there was a clear causal connection between at least two of the errors reported in an event report; if a report included three or four errors, the report might include an error cascade and an independent error.
‡Totals to more than 590 because multiple locations/actions taken were reported in some event reports.