Variables included in the study
| Variables | Type | Numerator | Denominator | Units | Transformation applied? | Interpretation |
| Breached attendances | Outcome | Number of ED attendances greater than 4 hours | Number of ED attendances | – | – | Proportion of ED attendances waiting >4 hours |
| Cancelled electives | Outcome | Number of cancelled elective operations | Number of elective admissions | Operations per admission | Log | Ratio of cancelled elective operations to elective admissions. In absence of the number of planned elective operations, this is the most suitable denominator |
| Empty day beds | Explanatory | Number of unoccupied day beds | Number of day beds | – | Categorised (5) | Ratio of unoccupied day beds to total number of day beds |
| Empty night beds | Explanatory | Number of unoccupied night beds | Number of night beds | – | Log | Ratio of unoccupied night beds to total number of night beds |
| Delayed transfers | Explanatory | Number of bed days taken by delayed transfers | Number of night beds | 10 bed-days | – | The number of bed-days lost to delayed transfers for each night bed at a trust, over the course of a year |
| Day bed:night bed ratio | Explanatory | Number of day beds | Number of night beds | – | – | Ratio of total day beds to total night beds |
| ED conversion ratio | Explanatory | Number of emergency admissions via ED | Number of attendances at ED | – | – | Ratio of ED admissions to attendances. Often commonly referred to as ‘conversion ratio’ |
| Admission casemix ratio | Explanatory | Number of non-elective (emergency) admissions | Number of elective admissions | – | Log | Proportion of admissions that are emergency or ratio of emergency to elective admissions |
| Emergency admission/bed ratio | Explanatory | Number of non-elective (emergency) admissions | Number of day and night beds | 10 admissions | – | Number of emergency admissions per bed over the course of a year |
ED, emergency department.