Opportunities for dispensing errors arise each time a prescribed medicine is dispensed. As with prescribed items, the same medicine dispensed monthly, or 12 different medicines dispensed from the same prescription, both represent 12 opportunities for dispensing errors.

Opportunities for administration errors arise every time a dose is administered or omitted in error, and so one medicine taken three times daily, or three medicines taken once daily, both represent three opportunities for error.

Opportunities for transition errors arise each time a discharge prescription is issued, regardless of the number of items on it.

*Opportunities for prescribing and monitoring errors arise each time an item is prescribed, so the same medicine prescribed monthly, or 12 different medicines on the same prescription, both represent 12 opportunities for prescribing and monitoring errors.

†Data are all from England.

‡Medicines prescribed and dispensed on discharge from hospital to primary care or care homes.

§Administration in primary care assumed to be patient-led and not under the control of healthcare professionals; this is generally referred to as “adherence”, and in this study we excluded any “errors” that might arise from suboptimal adherence.

¶Administered doses.

**Unweighted arithmetic mean derived from five UK studies set in specific patient populations; this includes both oral and parenteral administration6–10

N/A, not applicable.