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Prevalence Data in the Quality and Outcomes Framework

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Prevalence Data in the QOF

Data on the prevalence of specific diseases or conditions is an important element of the QOF. Prevalence is a measure of the burden of a disease in a population at a particular point in time (and is different to incidence, which is a measure of the number of newly diagnosed cases within a particular time period). Prevalence data are used within QOF to calculate points and payments within each of the clinical domain areas, and a number of the public health domain areas.
Specifically:
  • Points can only be awarded to a practice for a given domain area if the practice can produce a register of patients with the associated disease or condition, and
  • The number of pounds per point in each domain area is adjusted up or down according to each practice’s prevalence for each associated disease or condition, relative to the estimated regional Northern Ireland prevalence for that disease or condition.
Further details of the register definitions can be found below, and in the Statement of Financial Entitlement (Annex D) for each year of the QOF

Interpretation of the prevalence figures

The criteria for inclusion on the QOF registers can be very specific, and may not be comparable to other sources of prevalence data. For example the asthma register excludes patients who have not been prescribed asthma-related drugs in the previous twelve months. Care should be taken to understand definitional differences, for example when comparing QOF prevalence with expected prevalence rates using public health models.
Note that some of the clinical and public health domain areas are not measuring prevalence of a disease or condition.
For example the smoking indicators relate to the smoking status of people with one or more selected chronic conditions. The 'conditions assessed for smoking' register identifies how many patients at each practice have one or more of these conditions; the indicators cannot be used to determine prevalence of smoking.
Care should be taken when looking at trends in prevalence over time.
Year-on-year changes in the size of QOF registers are influenced by various factors including: changes in prevalence of the condition within the population; demographic changes, such as an ageing population; improvements in case finding by practices; and changes to the definition of the registers.
In several cases, the definition of the registers has changed over the years, for example, since April 2006 the definition of the epilepsy register has included patients aged 18 years and over, whereas previously it included those aged 16 years and over.
New registers should be treated with caution in the first few years of reporting as they are still being established and validated. Apparent increases in prevalence may be due to improvement in recording and case finding by GPs, rather than a true increase in the prevalence in the population.
The QOF prevalence figures presented here are raw prevalence rates. This means that they take no account of differences between populations in terms of their age or gender profiles, or other factors that influence the prevalence of health conditions. A QOF prevalence rate is simply the total number of patients on the register, expressed as a proportion of the total number of patients registered with a practice at one point in time. All prevalence registers are recorded as at National Prevalence Day each year. National Prevalence Day was initially 14 February each year; but from 2009 onwards National Prevalence Day was changed from 14 February to 31 March to bring it into line with National QOF Achievement Day.
The full registered list population is taken as at January of the relevant year, for example for 2004/05, the list size was taken at January 2005. The registered list population will differ from the mid-year estimate of population of Northern Ireland due to a combination of factors.
The definitions of some QOF registers are restricted to include only persons over a specific age. For QOF payment purposes, the QOF prevalence rates use as their denominator the total number of patients, of all ages, registered at January of the relevant year. This means that for these conditions the QOF-reported prevalence will appear lower than would be the case if the age restriction was also applied to the population denominator. For those indicators that have a specific age range, the raw prevalence is presented in both forms, calculated using the appropriate subset of the registered lists as the denominator for the age-specific register, in addition to the standard QOF prevalence calculated using the total number of patients of all ages.
Eight clinical areas within the QOF (diabetes, epilepsy, depression, chronic kidney disease, obesity, learning disabilities, palliative care and osteoporosis) are based on clinical registers that relate to specific age groups:
  • The diabetes register includes aged 17 years and over
  • The epilepsy  register includes patients aged 18 years and over, but included patients aged 16 years and over  prior to April 2006
  • The obesity register includes patients aged 16 years and over
  • The chronic kidney disease, depression, and learning disabilities registers include patients aged 18 years and over
  • The osteoporosis register includes patients aged 50 years and over, with an amended defintion for those aged 75 years and over
  • The rheumatoid arthritis register includes patients aged 16 and over

Limitations of the QOF data

The QOF data is only collected centrally at practice level. There is no centrally held data on patient details that can be directly linked to the prevalence registers, so the registers cannot be analysed by patient characteristics such as age or gender.  
The collection of the QOF data at an aggregate level for each practice also precludes robust analysis of co-morbidity. Many patients are likely to suffer from co-morbidity, i.e. they are diagnosed with more than one of the conditions included in the QOF clinical domain, but this cannot be analysed due to the lack of patient level data. For example, information is collected for each practice on patients with coronary heart disease and on patients with COPD, but it is not possible to identify or analyse patients with both of these diseases.

Register definitions

Register size and prevalence information is shown for 25 clinical indicators:
Coronary heart disease, stroke and transient ischemic attack, hypertension, diabetes, COPD, epilepsy, hypothyroidism, cancer, mental health, asthma, heart failure, heart failure due to LVSD, dementia, conditions assessed for depression, depression, chronic kidney disease, atrial fibrillation, obesity, learning disabilities, conditions assessed for smoking, palliative care, cardiovascular disease - primary prevention, osteoporosis, peripheral arterial disease, and rheumatoid arthritis.
QOF registers for 6 clinical areas have maintained consistent definition since April 2004: asthma, stroke and TIA, cancer, CHD, COPD, and hypertension.
The definition of diabetes, epilepsy and mental health changed slightly for 2006/07, and eleven new registers were introduced: atrial fibrillation, chronic kidney disease, dementia, heart failure 1, heart failure 3, conditions assessed for depression, depression, learning disabilities, obesity, palliative care, and conditions assessed for smoking.
The cardiovascular disease – primary prevention register was introduced in 2009/10, the osteoporosis and peripheral arterial disease registers were introduced in 2012/13, and a rheumatoid arthritis register was introduced in 2013/14.
Two of the registers first included in the QOF for 2006/07, palliative care and conditions assessed for smoking, were redefined for 2008/09. The conditions assessed for smoking register was further amended for 2012/13.
The new diagnosis of depression register, depression 2, was renamed to depression 4 in 2011/12 but the register definition was unchanged. The register was amended in 2012/13 and renamed to depression 6, changes to the register meant it was no longer comparable to previous years. For 2013/14 the register was renamed, but no changes were been made to the definition.
In 2013/14, the depression 1 register, conditions assessed for depression, was removed, and amendments were made to the hypothyroidism, mental health and heart failure due to LVSD registers.
  • Asthma: Number of patients with asthma, excluding those who have had no prescription for asthma-related drugs in the last 12 months.
  • Atrial Fibrillation: Number of patients with atrial fibrillation.
  • Cancer: Number of patients with a diagnosis of cancer, excluding non-melanotic skin cancers, from 1st April 2003.
    • Because of the date cut-off in the definition of this register, prevalence trends are obscured by the increase in the size of the register due to the cumulative accrual of new cancer cases onto practice registers with each passing year.
  • Cardiovascular Disease - Primary Prevention: Number of patients with a new diagnosis of hypertension (excluding those with pre-existing CHD, diabetes, stroke and/or TIA, peripheral vascular disease, familial hypercholesterolemia, or CKD) from 1 April 2009.
    • The definition of the CVD - PP indicator refers to patients aged 30 - 74 years with a new diagnosis of hypertension in the previous year, however the register is cumulative, and includes patients of all ages with a new diagnosis of hypertension since 1st April 2009.
    • As in the cancer register, because of the date cut-off in the definition of this register, prevalence trends are obscured by the increase in the size of the register due to the cumulative accrual of new cases onto practice registers with each passing year.
    • This register is not a count of those with CVD, it counts those who are at risk of developing the condition so that this risk can be assessed.
  • Coronary Heart Disease: Number of patients with coronary heart disease.
  • Chronic Kidney Disease: Number of patients aged 18 years and over with chronic kidney disease (US National Kidney Foundation: Stage 3 to 5 CKD).
    • Inclusion in the register is based on estimated Glomerular Filtration Rate (eGFR), a measure of kidney function. People with CKD stages 3 to 5 have, by definition, less than 60% of their kidney function.
  • Chronic Obstructive Pulmonary Disease (COPD): Number of patients with chronic obstructive pulmonary disease.
    • For 2004/05 and 2005/06 QOF definitions did not allow patients to be on both asthma and COPD registers thus patients with a degree of reversible airway disease were not included on the COPD register. From 2006/07 the rules were revised to allow patients to be included on both COPD and asthma registers. Approximately 15% of patients with COPD will also have asthma. Any comparisons of COPD prevalence before and after this change in definition should be made with caution.
  • Dementia: Number of patients diagnosed with dementia.
    • This indicator applies to all people diagnosed with dementia either directly by the GP or through referral to secondary care.
  • Conditions assessed for depression: Number of patients with diabetes and/or CHD.
    • Formerly known as Depression 1. This register was removed from the QOF from 2013/14.
    • The register figures do not represent numbers of people with depression, but counts people on the diabetes and/or CHD registers. The Depression 1 indicator then records whether patients with either or both of these conditions have been assessed for depression.
  • Depression: Number of patients aged 18 years and over diagnosed with depression since April 2006.
    • Although the Depression indicator definition does not refer to patient age, the QOF business rules define this register to include only patients who are aged 18 years and over.
    • The definition of the depression indicator was amended for 2011/12 as was therefore renamed from Depression 2 to Depression 4, however there was no change to the patients included on the register, so prevalence remained comparable to previous years. A further amendment was made for 2012/13 and the indicator was renamed as Depression 6. The register was therefore no longer comparable to previous years as patients diagnosed prior to April 2006 are now excluded. The register was renamed in 2013/14 but no further changes were made to the definition.
    • An unusual feature has been noted within the technical business rules that define how clinical IT systems count the register sizes for this indicator. Although the measurement of achievement against this indicator excludes patients diagnosed prior to the preceding 1st April, the pre-exclusion register size is used for prevalence purposes. For some practices with a long history of recording depression electronically in the clinical record (and where the depression was not recorded as having been resolved), a larger register size will have be reported for Depression 2/4 in comparison to an otherwise equivalent practice that had not been recording depression cases electronically over as long a time period.
    • The Depression register now has a date cut-off of April 2006, similar to the cancer register, therefore increases in the register size will, at least in part, be due to the cumulative nature of the register.
  • Diabetes Mellitus: Number of patients aged 17 years and over with diabetes mellitus (specified as type 1 or type 2 diabetes).
    • Since April 2006, the definition includes all patients aged 17 years and over with diabetes mellitus defined by clinical (Read) codes specific to Type 1 or Type 2 diabetes. Previously there was a wider range of codes accepted under the definition, although the age constraint has remained consistent. The prevalence statistics for 2006/07 onwards are therefore not directly comparable with those for 2004/05 and 2005/06.
    • Although the practice must record whether the patient has Type 1 or Type 2 diabetes, this level of detail is not collected centrally, therefore the register size cannot be disaggregated by type of diabetes.
  • Epilepsy: Number of patients aged 18 years and over receiving drug treatment for epilepsy.
    • Since April 2006, the definition of the register has included patients aged 18 and over, whereas previously it included those 16 and over. The prevalence statistics for 2006/07 onwards are therefore not directly comparable with those for 2004/05 and 2005/06.
  • Heart Failure: Number of patients with heart failure.
    • Also known as Heart Failure 1
  • Heart Failure due to LVSD: Number of patients with a current diagnosis of heart failure due to left ventricular systolic dysfunction (LVSD).
    • Also known as Heart Failure 3
    • The heart failure 3 register is a subset of the heart failure 1 register; all patients on the heart failure 3 register will also be included on the heart failure 1 register.
    • The Heart Failure 3 register originally included all patients with heart failure due to left ventricular dysfunction (LVD), from 2013/14 the definition was amended to include only patients diagnosed with left ventricular systolic dysfunction (LVSD), so the register is no longer comparable to previous years.
  • Hypertension: Number of patients with established hypertension.
  • Hypothyroidism: Number of patients with hypothyroidism who are currently treated with levothyroxine.
    • Initially this register included all patients with hypothyroidism, but from 2013/14 it was amended to exclude those who are not currently treated with levothyroxine so the register is no longer comparable to previous years.
  • Learning Disabilities: Number of patients aged 18 years and over with learning disabilities.
  • Mental Health: Number of patients with schizophrenia, bipolar affective disorder, and other psychoses, and other patients on lithium therapy.
    • Since April 2006, the definition has included only patients with serious mental illness, defined as schizophrenia, bipolar affective disorder or other psychoses. Previously, patient selection was based on more a more generalised set of mental health conditions and on the further condition that the patient required, and had consented to, regular follow-up. The prevalence statistics for 2006/07 to 2012/13 are therefore not directly comparable with those for 2004/05 and 2005/06. For 2013/14 the register definition was expanded to include other patients on lithium therapy, and the register is therefore no longer fully comparable with previous years.
  • Obesity: Number of patients aged 16 years and over with a Body Mass Index (BMI) greater than or equal to 30 recorded in the previous 15 months.
    • Not all people who are obese are recorded as such by general practices, particularly if they are young and have not experienced any particular health-related difficulties.  This register is prospective, and as a result apparent increases in prevalence may be due to improvement in recording and case finding by GPs, rather than a true increase in the prevalence in the population.
  • Osteoporosis: Number of patients aged 50-74 years with a record of fragility fracture after 1 April 2012 and osteoporosis diagnosis confirmed on DXA scan; or aged 75 years and over with a record of fragility fracture after 1 April 2012.
    • As in the cancer register, because of the date cut-off in the definition of this register, prevalence trends are obscured by the increase in the size of the register due to the cumulative accrual of new cases onto practice registers with each passing year.
  • Palliative Care: Number of patients in need of palliative care/support, irrespective of age.
    • Prior to April 2008, the register applied only to patients aged 18 years and over. The age restriction was removed so that the register now includes patients of all ages. This means that the figures for 2008/09 onwards are not directly comparable with those for earlier years. Due to the nature of palliative care, patients may only be only the register for a short period of time; as a result the practice palliative care register can only give an indication of the situation at the time the register was taken (prevalence day) and may not be a true reflection of practice prevalence throughout the rest of the year.
  • Peripheral Arterial Disease: Number of patients with peripheral arterial disease.
  • Rheumatoid Arthritis: Number of patients aged 16 or over with rheumatoid arthritis.
  • Conditions Assessed for Smoking: Number of patients with any or any combination of the following conditions: coronary heart disease, PAD, stroke or TIA, hypertension, diabetes, COPD , CKD, asthma, schizophrenia, bipolar affective disorder or other psychoses.
    • The smoking indicator reports on whether smoking status has been recorded for patients with one or more of these conditions, but the actual smoking status is not collected centrally. The ‘conditions assessed for smoking’ register records the number of patients suffering from one or more of these conditions, but the prevalence of smoking among these patients cannot be derived.
    • For 2006/07 and 2007/08 the register counted patients with any of the following conditions: CHD, stroke or TIA, hypertension, diabetes, COPD or asthma. In 2008/09, the definition of the register changed now includes CKD, schizophrenia, bipolar affective disorder and other psychoses in addition to the conditions listed above. The prevalence figures for 2008/09 to 2012/13 are not comparable to those from earlier years because of the inclusion of these extra conditions. For 2013/14 PAD was added to list of conditions, so the register is no longer fully comparable to previous years.
  • Stroke and Transient Ischaemic Attack (TIA): Number of patients with stroke or transient ischaemic attack (TIA).

Prevalence reports

Prevalence trend data

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