Seven acute trusts have emerged as consistent outliers against the controversial mortality rate measure, with significantly more patient deaths than expected, analysis of the latest data reveals.

The third summary hospital level mortality indicator (SHMI) data set was published by the NHS Information Centre last week, showing mortality rates for the year from October 2010 to September 2011.

Just nine trusts had higher than expected mortality rates in April’s data, compared to 14 in the first release last October and 11 in January.

Seven trusts – East and North Hertfordshire Trust, Basildon and Thurrock University Hospitals Foundation Trust, Colchester Hospital University Foundation Trust, Hull and East Yorkshire Hospitals Trust, Blackpool Teaching Hospitals Foundation Trust, George Eliot Hospital Trust and Tameside Hospital Foundation Trust – had higher than expected death rates in each of the first three publications of SHMI data.

Only Hull and East Yorkshire did not have a significantly higher than average proportion of admissions for palliative care.

Basildon, Colchester and East and North Hertfordshire had significantly more deaths than average coded as palliative. These are also the only three trusts found to be within the expected mortality range under the alternative hospital standardised mortality ratio measure produced by Dr Foster.

Unlike the SHMI, the Dr Foster measure adjusts for the proportion of patients coded as palliative on admission and at death.

The variation suggests that although palliative care may be a factor in some of the outliers it is not the only cause.

All the outlier trusts said they had examined in detail the reasons for their inclusion on the SHMI outlier list since the figures were first published last year. East and North Herts and Basildon highlighted palliative care as the main issue.

The DH-commissioned steering group set up to develop the SHMI and bring consensus to the contested area of mortality rates decided against adjusting for palliative care due to the huge variation in how the coding is used.

According to supporting data published alongside the latest SHMI, the percentage of admissions coded as palliative ranged from 0-3.2 per cent across trusts while the percentage of deaths classified as palliative ranged from 0 to 41.6 per cent. However, experts have questioned whether that variation can reflect reality or the coding practice.

King’s Fund senior fellow Veena Raleigh, a member of the steering group, told HSJ the methodology could be altered to take into account palliative care in future if guidance was produced on how the code should be used which reduced variation.