Results listed are from five separate conditional logistic regression models, each with ward fixed effects. Unit of analysis is the hospital ward-day (n=19 287). HCSWs, defined as those in NHS pay bands 2–4. RNs, defined as those in NHS pay band 5 and above. 95% CI, with SEs clustered at the hospital ward level. All models also control for the mean patient age; the patient age squared; the sex and ethnicity mix of patients; the mean Elixhauser Comorbidity Index; pairwise-interaction terms between mean age, sex, ethnicity and Elixhauser Comorbidity Index; the mean hospital length of stay of patients treated in the ward that day; the number of patients treated in the ward that day; a dummy for each day of the week; a dummy for month of the year and a dummy indicating whether the day was a bank holiday. Fill-rate is defined as the number of actual hours worked divided by the number of planned (rostered) hours. The fill-rate for healthcare support workers and registered nurses is calculated relative to the planned hours for staff of that type.

NHS, National Health Service; ppt, percentage point.