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Audits > Clinical audit information > Data analysis and methodology

Data analysis and methodology

Patient data collected by SSNAP is analysed centrally by the programme with an array of reporting outputs produced in the weeks following each data-locking deadline. Some of the key terminology and methodology used for SSNAP analysis are outlined below.

Analysing ‘locked’ data only
Only ‘locked’ data are included in SSNAP analysis. The process of locking ensures high data quality and signifies that the data have been signed off by the lead clinician and are ready for central analysis. SSNAP records can be locked at three levels depending on their level of completion: ‘locked to 72 hours’ for patients who have received their acute care provision; ‘locked to discharge’ for patients who have been discharged from one or more care providers’; and ‘locked’ to 6 months for patients whose 6 month assessment status has been recorded.

‘Patient-centred’ and ‘team-centred’ results 

SSNAP reports on the processes of care and patient outcomes in two ways; ‘patient-centred’ and ‘team-centred’. ‘Patient-centred’ results are attributed to every team which treated the patient at any point in their inpatient care. A team’s patient-centred results demonstrate the quality of care that their patients received across the whole inpatient care pathway, regardless of how many teams cared for the patient, or which of the teams provided each aspect of care. ‘Team-centred’ results attribute to the team considered to be the most appropriate to be responsible for a given measure.

Categorisation of stroke services

SSNAP divides participating teams into the following categories for reporting purposes:
Inpatient teams:
  • Routinely admitting acute teams: teams which admit stroke patients directly for acute stroke care
  • Non-routinely admitting acute teams: teams which do not generally admit stroke patients directly but which continue to provide care in an acute setting when patients have been transferred from their place of initial treatment
  • Non-acute inpatient teams: teams which provide inpatient rehabilitation in a post-acute setting, such as community hospitals
Non-inpatient teams:
  • Post-acute non inpatient teams: teams which provide early supported discharge (ESD) and community rehabilitation
  • 6-month assessment providers: community based teams which provide reviews at 6 months

Tiers of analysis and reporting

SSNAP analyses clinical audit data at a number of different levels to engage as wide an audience as possible. This involves reporting at hospital, regional, national and population level.
  • Hospital or ‘team’ level analysis: This includes aggregate-level patient data at individual service or ‘team’ level for the relevant reporting period.
  • Regional level analysis: This brings together hospital or ‘team’ level analysis on a regional basis. Services in England are grouped by the Integrated Stroke Delivery Networks (ISDNs) to which they belong. Wales and Northern Ireland are each reported as a region.
  • National level analysis: This includes all patient data for England, Wales and Northern Ireland aggregated together to provide national level results.
  • Population or ‘CCG/LHB’ level analysis: This includes aggregate-level patient data but rather than assigning patients to the stroke service where they were treated they are assigned to their clinical commissioning group (CCG) or local health board (LHB). This is achieved by linking patients’ home postcodes to that of the relevant CCG or LHB. In this way specific population-level reporting of stroke care is possible. Integrated Care Boards (ICBs) were established on 1 July 2022 and CCGs closed down. Future reporting outputs will be based on ICBs. As postcode is not collected in Northern Ireland, population-level analysis cannot be conducted for this region.

Statistical terminology

The following abbreviations are used within SSNAP reports:
  • ‘d’ is the denominator, or total number of patients the question refers to. Note that not every question applies to every patient. For example, the denominator for ‘If AF before stroke, on anticoagulant medication’ only includes those patients with atrial fibrillation before their stroke. 
  • ‘n’ is the numerator, which  can be the number of patients whose care met a standard, or the number of people in a particular category.
  • ‘%’ is the percentage of patients. The percentage is calculated as the numerator divided by the denominator, multiplied by 100. It can be the percentage of eligible patients whose care meets a standard (e.g. the percentage of patients scanned within 1 hour of clock start), or the percentage of patients in a particular category (e.g. the percentage of patients whose first ward of admission was an MAU/AAU/CDU).
  • ‘Mean’ is the average results where all results are added together and then divided by the number of results. The mean is another way of describing the average result. It can be particularly useful if the total time is of interest – for example, the mean length of stay in hospital from clock start to discharge from inpatient care.
  • ‘Median’ is the middle patient's result for the question, that is, half of patients have a higher result, and half of patients have a lower result. It is one way of describing the average result.
  • ‘Lower IQR and upper IQR’ gives the interquartile range (IQR) of patients' results. Results are divided into four quarters, two below and two above the median. One quarter of all patient’s results are lower than the lower IQR, one quarter of results are within the lower IQR, one quarter are in the upper IQR and one quarter are above the upper IQR. The IQR gives an indication of the variation between patients for a given question.

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Sentinel Stroke National Audit Programme
Kings College London
Addison House
Guy's Campus


0116 464 9901