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BackupV1 > About SSNAP > SSNAP Clinical Audit > Data Analysis Methodology

Data Analysis Methodology

Stroke 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 terminologies 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 provider; ‘locked to six months’ for patients for patients for whom 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’ attribute the results to every team which treated the patient at any point in their 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 each patient went to, or which of the teams provided each aspect of care. ‘Team centred’ attribute the results to the team considered to be most appropriate to assign the responsibility for the measure to.

Categorisation of stroke services

SSNAP divides participating teams into the following categories for reporting purposes:
  • 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 continue to provide care in an acute setting when patients have been transferred from place of initial treatment
  • Non-acute inpatient teams: teams which provide inpatient rehabilitation in a post-acute setting e.g. community hospitals
  • Post-acute non inpatient teams: these teams include early supported discharge and community rehabilitation teams
  • Six month assessment providers: community based teams that provide six month reviews
Tiers of analysis

The clinical component of SSNAP analyses at a number of different levels to engage as wide an audience as possible. This includes hospital, regional, national, and population level reporting.
  • 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 includes aggregate level patient data at service level with teams being grouped according to the region in which they are based. Services in England are regionalised by the strategic clinical network (SCN) to which they belong. Wales and Northern Ireland are also reported as separate regions.
  • 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 the clinical commissioning group (CCG) or local health board (LHB) in which they belong. 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. For more details go to the ‘methodology’ section of any CCG/LHB level reports available here
Statistical terminologies

The following abbreviations are used within SSNAP reports:
  • "d" is the denominator. The denominator is the total number of patients the question refers to. For questions where only some patients are applicable, the denominator tells you how many of the patients the question refers to. For example, the denominator for "If AF before stroke, on anticoagulant medication" is based only on those patients who were in Atrial Fibrillation before stroke. 
  • "n" is the numerator. The numerator can be the number of patients who actually received the standard, or the number of people who are in a particular category.
  • "%" is the percentage of patients. The percentage is calculated as 100*numerator/denominator. It can be the percentage of eligible patients who received 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).
  • "Median" is the middle patient's result for the question. The median patient's result is where half of patients would have a higher result, and the other half of patients would have a lower result. It is one way of describing the average result.
  • "Lower IQR and Upper IQR" give the interquartile range (IQR) of patients' results. Half of all patients' results lie within the IQR, and a quarter of results are lower than the Lower IQR, and a quarter of results are higher than the Upper IQR. The IQR therefore gives you an indication of the variation between patients for each question.
  • "Mean" is the average result 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.

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


0116 464 9901