Events: Term stillbirths and term neonatal deaths (up to 28 days)

National reference rate: The total number of events in England divided by the total number of births.

Excess events: The cumulative number of events over time in excess of the national reference rate.

CUSUM: Cumulative Sum. A statistic based on the cumulative variation between the number of events over time and the expected number of events based on the national reference rate.

Statistical confidence: How certain we are that a signal is true if the measurement was repeated many times.

Level 1: A 95% statistical confidence that the rate of events has at least doubled the trust site’s expected rate of events. Data points plotted above this threshold are ‘level 1’ amber signals.

Level 2: A 99% statistical confidence that the rate of events has at least doubled the trust site’s expected rate of events. Data points plotted above this threshold are ‘level 2’ red signals.

Reset: Applicable to the CUSUM chart only. After a level 2 signal, the trust site rate of events is reset to 0. This is to allow the chart to remain sensitive to future signals.

Critical safety check: Trust sites must carry out a ‘critical safety check’ of their intrapartum service immediately following a signal. This is contained in Annex 1 of the standard operating procedures for MOSS.

Publication reference: PRN02098_ix