Medical and Information
Intelligent Information: A National
System for Monitoring Clinical
Alex Bottle and Paul Aylin
Objective. To use statistical process control charts to monitor in-hospital outcomes at
the hospital level for a wide range of procedures and diagnoses.
Data Sources. Routine English hospital admissions data.
Study Design. Retrospective analysis using risk-adjusted log-likelihood cumulative
sum(CUSUM) charts, comparing each hospitalwith the national average and its peers for
in-hospital mortality, length of stay, and emergency readmission within 28 days.
Data Collection. Data were derived from the Department of Health administrative
hospital admissions database, with monthly uploads from the clearing service.
Principal Findings. The tool is currently being used by nearly 100 hospitals and also a
number of primary care trusts responsible for purchasing hospital care. It monitors
around 80 percent of admissions and in-hospital deaths. Case-mix adjustment gives
values for the area under the receiver operating characteristic curve between 0.60 and
0.86 for mortality, but the values were poorer for readmission.
Conclusions. CUSUMsare a promisingmanagement tool formanagers and clinicians
for driving improvement in hospital performance for a range of outcomes, and interactive
presentation via a web-based front end has been well received by users. Our
methods act as a focus for intelligently directed clinical audit with the real potential to
improve outcomes, but wider availability and prospective monitoring are required
to fully assess the method’s utility.
There is an ever-increasing focus on monitoring clinical standards in many
countries’ health services, including measures of process (such as administration
of prophylactic antibiotics), outcome (such as mortality), and safety (adverse
events and patient satisfaction). Data are commonly taken fromhospitals’
administrative data sets, from other bodies such as national clinical audits, or
collected specifically for the measurement of performance indicators. The
r Health Research and Educational Trust
DOI: 10.1111/j.1475-6773.2007.00742.x
range, type, construction, and use of such indicators vary greatly across countries,
although some, such as mortality following acute myocardial infarction,
are likely to be common to many westernized nations due to the (relative)
‘‘hardness’’ of the endpoint (death) and of the diagnosis and because there is a
sound evidence base regarding treatment protocols.
Wedescribe a performance monitoring tool used by nearly 100 National
Health Service (NHS) hospitals in England (Dr. Foster Intelligence 2005). We
begin by outlining the main approaches in the United States and the United
Kingdom in terms of who sets the clinical standards, what metrics and benchmarks
are used to assess performance, and how the feedback loop is closed,
before presenting the tool. We first describe the role of the tool and how it fits
in with existing U.K. policy, the types of user and some examples of how the
tool has been used by hospitals to improve their outcome rates. We then give
the technical details covering the data sources, the outcome measures monitored
and statistical methods regarding the statistical process control charts
including a consideration of case-mix adjustment, and how the results might
be acted upon (operationalized) by a hospital using the scheme.
Setting of Standards
The Joint Commission on Accreditation of Healthcare Organizations is the
nation’s predominant standards-setting and accrediting body in health care.
Accreditation by the Joint Commission is recognized nationwide as a symbol
of quality that indicates that an organization meets certain performance standards.
Also important is the National Quality Forum, created in 1999 to ‘‘improve
American health care through endorsement of consensus-based
national standards for measurement and public reporting of health care performance
data.’’ Their ‘‘Compendium 2000–2005’’ covers all their endorsed
measures and standards (Quality Forum 2006).
To determine whether health care plans meet these standards, the calculation
of measures is required, and the choice and use of these measures come not
from the institutions that created them but from government bodies such as the
Centers for Medicare and Medicaid Services (CMS) and the purchasers of care.
Address correspondence to Alex Bottle, Ph.D., Dr. Foster Unit at Imperial College, Department of
Primary Care and Social Medicine, Imperial College London, First floor, Jarvis House, 12 Smithfield
Street, London EC1A 9LA, U.K. Paul Aylin, M.B., Ch.B., F.F.P.H.M., is with the Dr. Foster
Unit at Imperial College, Department of Primary Care and Social Medicine, Imperial College
London, London, U.K.
National System for Monitoring Clinical Performance 11
Assessment of Meeting Standards
In 1997, the Joint Commission launched ‘‘ORYX: The Next Evolution in
Accreditation’’ to integrate the use of outcomes and other performance measures
into the accreditation process ( Joint Commission on Accreditation of
Healthcare Organizations 2006). A component of the ORYX initiative is the
identification and use of standardized (‘‘core’’) performance measures; accredited
hospitals began collecting data on these in 2002. The hospital core
measures for 2006 covered acute myocardial infarction, heart failure, pregnancy
and related conditions, pneumonia, and surgical infection prevention.
To earn and maintain accreditation, an organization must undergo a regular
on-site survey by a Joint Commission survey team at least every 3 years.
However, hospitals pay for Joint Commission surveys, and more than 70
percent of the Joint Commission’s revenue comes directly from the organizations
it is supposed to inspect (American Federation of Teachers 2006). The
Joint Commission have switched to unannounced inspections for all hospitals
during the 3-year cycle, but these have been criticized for being superficial and
failing to detect significant hospital safety and performance problems——identification
of poor care patterns are not distinguishable by the Full Survey score
or by the accreditation decision (United States Government Accountability
Office 2004; Moffett, Morgan, and Ashton 2005).
The Agency for Healthcare Research and Quality (AHRQ) has developed
a large number of quality indicators such as mortality rates for stroke and
coronary artery bypass graft (CABG) for use with hospital data that can enable
hospitals and also federal and state policy makers to track performance over
time (AHRQ 2006). These were developed and expanded from the Healthcare
Cost and Utilization Project, which aims to build uniform databases from
hospital-based administrative data. The Agency also supplies software to
calculate the indicators of interest to a given hospital once that hospital has
extracted the necessary data.
When large employers purchase health care for their staff, they want
value for money, which has led to the National Committee for Quality
Assurance (NCQA) overseeing the Health Plan Employer Data and Information
Set (HEDIS). This is a tool used by more than 90 percent of America’s
health plans to measure performance on important dimensions of care and
service (NCQA 2006a). Health care plans are given scores for 17 different
performance measures. These include how well the plans manage high blood
pressure or how precisely they adhere to clinical evidence-based protocols.
The NCQA publish their national benchmarks and national and regional
12 HSR: Health Services Research 43:1, Part I (February 2008)
thresholds for HEDIS measures for each accreditation year (NCQA 2006b).
NCQA determines the HEDIS measures’ portion of the score by comparing
the provider’s results with the benchmark of the 90th percentile of national
results and with regional and national thresholds (the 75th, 50th, and 25th
percentiles). CMS accreditation uses similarly calculated HEDIS benchmarks
and thresholds.
The most prominent example of providers themselves measuring performance
in order to improve is the nation’s largest health care provider, the
Department of Veterans Affairs. Beginning in the early 1990s, they established
system-wide quality improvement initiatives, many of which the Institute of
Medicine would later recommend. An example is their National Surgical
Quality Improvement Program, which uses performance measurements,
reports, self-assessment tools, site visits, and best practices (American College
of Surgeons 2006).
Publication and Completing the Feedback Loop
If hospitals do not meet the prescribed standards, then CMS can withdraw
their accreditation and eligibility for federal hospital funding and the Joint
Commission may withdraw their accreditation, leading to the loss of private
health carrier reimbursements, until corrective changes are made.
A recent important development is the emergence of pay for performance.
Some organizations such as CMS have incorporated selected AHRQ
indicators into this process. In the Premier Hospital Quality Incentive Demonstration,
hospitals scoring in the top 10 percent for quality measures relating
to five clinical conditions will receive a 2 percent bonus payment on top of the
standard DRG payment. Those scoring in the next highest 10 percent will
receive a 1 percent bonus. In the third year of the project, those hospitals that
do not meet a predetermined threshold score will see their payments reduced
(CMS 2005). Hospital-specific performance will be publicly reported on
CMS’s website. The project is a demonstration and involves the voluntary
participation of over 260 hospitals and is designed to determine if financial
incentives are effective at improving the quality of inpatient hospital care.
Patients can access a web-based program called Hospital Compare
(Hospital Quality Alliance and the United States Department of Health and
Human Services 2006) to see how any given participating hospital compares
for heart attack, heart failure, pneumonia, and surgery indicators with the
averages for the nation, the state, and the top 10 percent of hospitals. Data are
provided by the Hospital Quality Alliance, which encourages hospitals to
National System for Monitoring Clinical Performance 13
collect and publish their data voluntarily. Graphs for the hospital with the
three comparisons drawn on are shown, with tables giving the denominators.
Setting of Standards and Targets
The 24 (with component parts) ‘‘core’’ standards for providers of NHS services,
such as ‘‘Healthcare organizations must enable all members of the
population to access services equally and offer choice in access to services and
treatment equitably,’’ outline the acceptable level of care as set by the
Department of Health, who also set the current national targets in 2004 (Department
of Health 2004). These comprise standards that all health care
organizations in England that treatNHS patients should be achieving now and
‘‘developmental standards’’ that they should be aiming to achieve in the future.
It is the responsibility of trust boards to satisfy themselves that they are
meeting core standards and, where this is not happening, to take appropriate
steps to correct the situation (Healthcare Commission 2005a).
Assessment of Meeting Standards and Targets
In the United Kingdom until 2005, hospitals were compared using the star
rating system of the Healthcare Commission, originally the Commission for
Healthcare Improvement, an independent body set up to promote and drive
improvement in the quality of health care and public health (Healthcare
Commission 2006a), charged with assessing the performance of every NHS
hospital trust and private health care provider. This system awarded each
NHS hospital up to three stars by combining a large number of diverse indicators
covering a range of services, varying from the administrative, such as
financial management, to the clinical, such as waiting times for referral for
suspected cancer. Each hospital was assigned to one of five bands according to
the position relative to the national average of three different confidence intervals
(CIs) around the rates. Hospital results were available online as a band
for each indicator or the overall number of stars (Healthcare Commission
2005b). This has been replaced with the ‘‘annual health check,’’ based upon
measuring performance within the Department of Health framework of national
standards and targets and intended to be more ‘‘patient centered’’ (Day
2006). Core standards, existing national targets, use of resources and new
national targets are scored separately. The responsibility is placed on boards of
trusts to make a self-assessment and public declaration on the extent to which
14 HSR: Health Services Research 43:1, Part I (February 2008)
their organization has met the core standards. To measure performance
against the 21 existing national targets, the Healthcare Commission used 26
different indicators in the 2005/2006 annual health check, with 13 applicable
to acute and specialist hospital trusts, such as whether the patient waited more
than 3 months for revascularization or more than 4 hours in accident and
A number of indicators, such as mortality following heart bypass and
emergency readmissions following hip fracture, are derived from routine administrative
data (Hospital Episode Statistics [HES]) that all NHS hospitals are
mandated to collect and submit at least quarterly to the Department of Health.
Our tool also uses these data. The set of indicators is also informed by the
‘‘better metrics project,’’ begun in 2004 to improve the clinical relevance of
NHS performance assessment measures, and to date covering 11 clinical areas
and health inequalities (Whitty et al. 2006). The annual health check has two
elements: quality and use of resources. The quality element sums the scores for
the assessment of whether core standards and existing or new national targets
are met, using the following four-grade scale: ‘‘fully met,’’ ‘‘almost met,’’
‘‘partly met,’’ or ‘‘not met.’’ In terms of quality overall, hospital trusts are then
rated as ‘‘excellent,’’ ‘‘good,’’ ‘‘fair,’’ or ‘‘weak.’’
Publication and Completing the Feedback Loop
The Healthcare Commission checks these annual health check self-declarations
against a wide range of surveillance information and will follow up if
there are discrepancies between the two sources; after the 2005/2006 results,
60 out of a total of 570 NHS trusts were inspected for this reason, with another
60 inspected after being chosen at random. The inspections looked at whether
the documentary evidence that the trusts relied upon when making their declarations
was adequate. Following inspection, recommendations were made
and outcome measures by which the practice changes would be judged were
described. Results by health care provider from the annual health check (and
its predecessor) are freely available on the Internet.
A recent addition to publicly accessible hospital performance data covers
survival following cardiac bypass and aortic valve replacement using data
from the Society for Cardiothoracic Surgeons in Great Britain and Ireland
(Healthcare Commission 2006b). This gives risk-adjusted survival rates by
center and named surgeon, though the data are not easy to extract and the
Society admits that, as it used EuroSCORE for risk adjustment, risks are
overpredicted due to technical improvements in surgery and anesthetics.
National System for Monitoring Clinical Performance 15
The Society has recently introduced a voluntary accreditation scheme, involving
site visits and comparison of risk-adjusted outcome rates against
the Society’s targets, with mechanisms of dealing with underperformance
(Cardiothoracic Surgery Network 2004).
Private Hospitals
Private hospitals (i.e., those not in the NHS) are most commonly used for
elective surgery in the United Kingdom. The Healthcare Commission currently
has a statutory obligation to inspect all independent sector registered
establishments at least annually, and is continuing to develop the process for
registering and inspecting. They have recently developed a series of high-level
indicators to help monitor the performance, such as overall perioperative
mortality and surgical site infections. Some of this information is also submitted
to bodies such as the Independent Healthcare Forum (as part of their
credentialing program for the private sector) and the U.K. arm of the Quality
Indicator Project, which originated in the United States and now operates in
12 countries (U.K. Quality Indicator Project 2006). Our system does not yet
cover private hospitals as we do not have the data.
We view our system as complementary to government-led performance
monitoring. As well as being voluntary to join, it does not detail improvements
to processes that must be made, whereas participation in the regulator’s ‘‘annual
health check,’’ like the star ratings system before it, is mandatory and focuses
on processes. Rather, our tool flags particular diagnoses or operations with
significantly high (or low) outcome rates at the user’s unit. Unlike with Hospital
Compare and the ‘‘annual health check,’’ output from our tool is not published.
We have chosen to concentrate on outcome measures as these are
generally what matters most to the patient and are easier to measure from
routine data. The onus is then on the user to investigate further as described
later, beginning with subanalyses using the tool and proceeding to inspection
of case notes and processes along the care pathway within the hospital. If
managers and clinicians are serious about improving quality, they will not
ignore the tool’s findings. If quality of care is found to be substandard to the
point of leading to undesirable outcomes, then improvement efforts may be
assessed over time using the tool.
16 HSR: Health Services Research 43:1, Part I (February 2008)
As well as hospital trusts, the system is also used by primary care trusts
and strategic health authorities. Among their primary responsibilities is the
assessment of their patients’ needs and purchasing hospital care for them.
Although there is no competitive market for emergency care in the United
Kingdom, hospitals do now effectively compete for contracts for elective work
with the private sector and in particular the new Independent Sector Treatment
Centres. Strategic health authorities can demand value for money from
hospitals that serve their patients, and there is particular focus currently on
reducing inappropriately long length of stay, thereby reducing costs. One
strategic health authority has asked all its hospital trusts to sign up to our tool
for this reason (see ‘‘real-world examples of use’’). More and more hospitals
are seeking to become Foundation Trusts, which gives them, for example,
more financial autonomy from the government while remaining within the
NHS, but applications to become Foundation Trusts are only accepted from
top-performing hospitals. One hospital trust has used benchmarking results
from our tool as part of their application. These policies combine to put
pressure on hospitals to improve their outcomes.
Procedure-Specific Mortality Alarms
The medical director of one hospital trust was alerted by an alarm (when the
chart crosses the threshold——see ‘‘Tool Methodology’’ for details on chart
construction) on their alarm screen (as in Figure 2) for high in-hospital mortality
for lower gastrointestinal surgery. On further analysis using the tool’s
drill-down (cross-tabulation) capability, it was clear that emergency admissions
occurring on some days of the week had a significantly higher risk of
death than on others. A review of the rota system revealed that the most
experienced surgeons were not available at these times for operating on the
most severe cases. The rota was changed to allow the most experienced surgeons
to be free to cover for these days. Mortality has since dropped to average
levels, with no further chart alarms.
Disease-Specific Readmission Alarms
The Director of Performance and Development at another trust followed up
an alarm regarding readmissions for chronic obstructive pulmonary disease.
Activity was reviewed for a 9-month period. There were 87 readmissions
National System for Monitoring Clinical Performance 17
against an expectation of 71. A review of the notes identified that six patients
accounted for 31 admissions and that there were significant clinical factors
associated with each case. It was concluded that these patients did indeed have
severe disease that warranted the extra hospitalizations and that no further
action was required.
Mortality Alarms Involving Multisite Hospitals
Two hospitals with high overall mortality demonstrated by the tool decided on
more far-reaching action. Walsall Hospitals NHS Trust’s medical director and
others formed seven clinical governance groups to implement changes in
several clinical disease areas. Similarly, changes were initiated in several
management areas including audit department, clinical risk, continuing professional
development unit, bed management, and information services, and
the significant decrease in mortality can be seen on the tool ( Jarman et al.
2005). Bradford Teaching Hospitals NHS Trust established a hospital mortality
reduction group with senior leadership. The tool was used with death
certificates and local routine hospital data to review progress. There was extra
training in areas such as clinical observation, medication safety, and infection
control (Wright et al. 2006).
Length of Stay Alarms Involving Multiple Hospitals
Another type of user is the Strategic Health Authority, of which there
are currently 10 in England, with responsibility for clinical governance
and in getting the best care for patients within its boundaries. One such
Authority asked all its hospital trusts to sign up for the tool and found
that many of its acute trusts had a lot of alarms for length of stay. As they
drilled down, they found that short lengths of stay were associated with
better clinical outcomes. After retrieving case notes and checking the
data, long lengths of stay in some cases were due to delays in accessing
investigations and, at its worst, sometimes led to increased mortality.
One example of this was the treatment of fractured neck of femur. The tool
enabled them to analyze mortality and length of stay by preoperative length
of stay, a measure which, if prolonged, has been found to be associated with
higher mortality (Bottle and Aylin 2006). Some of the Authority’s acute
trusts had average lengths of stay of up to 36 days, but in 6 months that
particular trust reduced its average from 36 to 18 days by focusing on the
clinical pathway.
18 HSR: Health Services Research 43:1, Part I (February 2008)
We now describe how the user, usually hospital managers but also senior
clinicians, accesses the system, requests the desired analyses, and then
‘‘operationalizes’’ the results by investigating a chart alarm and completing the
When the user gets past the log-in screen after typing in their user name
and password supplied by the system administrator, they see a grid with
diagnosis and procedure groups as rows and outcome measures as columns,
with each cell containing either a red bell symbol if the chart has crossed the
threshold for an odds ratio (OR) of 2 in the last 3 months, suggesting a high
outcome rate, or a green bell symbol if the chart has crossed the threshold for
an OR of 0.5, suggesting a low outcome rate. If the threshold has not been
crossed for a given diagnosis or procedure, the cell is not shown (Figure 1).
Clicking on a bell will display the relevant chart (see ‘‘Tool Methodology’’)
with an accompanying table of figures giving observed and expected outcomes
with CIs for the monitored period. Charts are plotted chronologically
Figure 1: Screenshot of Online Monitoring System Front Page That the User
Sees after Logging In
National System for Monitoring Clinical Performance 19
and will come to a stop at the most recent patient, whose date of discharge may
be read from the chart.
Each alarm is a starting point for action. In the ideal scenario, all alarms
would represent genuine problems with performance, but in practice some
will be false alarms. These could be considered to be of two types. ‘‘Statistical’’
false alarms, in which the trust’s outcome rate is in fact compatible with the
national average but the trust has had a run of ‘‘bad luck,’’ i.e. the alarm
occurred by chance; these can be minimized by raising the chart threshold.
Further alarms after resetting the chart rather than a single alarm would suggest
a genuinely high rate. ‘‘Medical’’ false alarms occur when the odds of the
outcome of interest are at least twice the benchmark but the cause is not one of
poor quality of care.
In real practice, however, we do not know if an alarm is false (what in
screening terms would be called a false positive) or the detection of an outcome
with at least twice the benchmark odds (true positive, though some of
these will be medical false alarms).
The following has been suggested as a ‘‘check list’’ for the hospital leaders
following up an alarm (Marshall and Mohammed 2002; Lilford et al.
(1) Check data quality.
(2) Assess the case mix.
(3) Consider policy or organizational (‘‘process of care’’) issues
(‘‘structure’’ in Lilford and colleagues’s pyramid).
(4) Quality of care.
After an alarm, the probability of a false alarm given the number of
patients monitored and underlying outcome rate can be displayed from tables
of results from prerun simulations. If this is felt to be high, then the chart may
be reset with no further action. If not, or if the chart again crosses the threshold
soon after it first does so, then the data quality should be checked, for example
using the data quality report that is part of our tool (e.g., to see if a high
proportion of records have been excluded due to invalid or duplicate entries)
and then by comparing the admissions and outcomes on the tool with first the
hospital’s electronic records and then the patient notes.
If the first stage does not reveal an explanation for the alarm, the second
step is to examine the case mix of the patients, for example by auditing a
random sample. Clinicians may be aware of other case-mix issues such as
specializing in palliative care. At this stage, organizational issues can be considered
such as the appropriateness of referral and delays in admission beyond
20 HSR: Health Services Research 43:1, Part I (February 2008)
the control of the hospital. If these can be excluded or are found to be of
insufficient magnitude to explain the high outcome rate, then quality of care
could be the explanation, from inappropriate referral and preoperative care
through to peri- and postoperative care. Drop-down menus guide the
user to selecting the time period, age range, weekday of admission, and many
other factors to see if the alarm affects all patients with the diagnosis or procedure
or just a subgroup. The time period of monitoring can be extended
back to any time from 1996 in order to see if the trust has had an earlier alarm
and how many it had to see how long-standing the potential problem is. Data
can be viewed by individual named consultant (depending on the access
privileges set by the administrator) and compared with others in the same
Although the national average is used for all inpatient benchmarks, each
trust can compare itself with six of its peers, defined as having either similar
volume by the user themselves, or the six best performers in a table giving the
relative risks for each trust.
After looking at aggregate admission counts and observed and expected
outcomes, the authorized user (with access to specific patient data) can view
the complete electronic record for each admission, including all diagnoses and
procedures, dates, age, sex, and outcomes, which can be downloaded into
Excel. This can help with validation of the electronic data against the patient
notes (item 1 on the above check list) and a starting point for considering casemix
issues (item 2) and then the care pathway (items 3 and 4).
Data Sources
HES are routinely collected data that cover all inpatient and day case admissions
to NHS hospitals in England. The monitoring tool uses 9 years of admissions
data from 1996/1997 to 2004/2005, covering acute and community
hospital trusts (a trust can consist of several hospitals, each with their own site
code). These are augmented by monthly submissions from each trust via the
NHS-wide Clearing Service (a data warehouse) from April 2005 so that data
are at most 6 weeks out of date at any time.
Each of the 14 diagnosis fields is coded using ICD10 and we assign it to
one of 259 clinically meaningful groupings using the AHRQ’s CCS classification
(Agency for Health Care Policy and Research 2003). The 12 operation
fields use U.K. OPCS4 codes (Office of Population Censuses and Surveys
National System for Monitoring Clinical Performance 21
1990), of which the first is usually the most major even if it was not the first to
be performed. No grouping scheme for OPCS4 codes currently exists, and we
have therefore grouped them together after taking clinical advice from a
number of professional bodies (e.g., the Vascular Surgical Society). Not all
diagnosis and procedure groups have enough numbers to enable robust comparisons
and the tool monitors 77 diagnosis and 102 procedure groups.
Groups were usually chosen for monitoring if they had large numbers of
deaths or admissions, but a few less common procedures were requested by
clinicians. The diagnosis groups cover over 80 percent of deaths and admissions,
and the procedure groups about 70 percent of deaths and 80 percent of
admissions with some procedure recorded.
The basic unit of the database is the consultant episode, the continuous
period of time during which the patient is under the care of a particular
consultant, whose registration number is recorded, enabling consultant-level
analysis. In an admission, a patient can have any number of episodes, though
around 85 percent have only one. Episodes are linked together into admissions
if they belong to the same patient and have the same admission and
discharge date at the same trust, and admissions are linked together to account
for interhospital transfers.
The diagnosis used for monitoring is the first field (‘‘primary diagnosis’’)
for the first episode, i.e., on admission, although if there is only a vague
symptoms and signs diagnosis in this episode, a diagnosis is taken from the
subsequent episode (if there is one). All outcome measures are assigned to this
diagnosis as the reason for admission is usually of most interest. The procedure
used for monitoring is usually the first nonmissing procedure field containing
one of the codes in Table 1, with some extra rules concerning cardiac
procedures, e.g., CABG takes priority over cardiac catheterization.
Availability and Quality of Data. Ideally, the statistical process control charts
could be constructed in real time from patient administration system data so
that any necessary remedial action may be taken as early as possible. During
the current financial year, hospitals are able to resubmit data, if, for example,
they have updated their diagnostic coding. There is considerable variation
between hospitals in the frequency of data submission to the clearing house
and in the quality of the most recent submission. Clearly, trusts that are able
to submit good quality data on time will detect potential problems earlier
than others.
One of the features of our tool is the display of basic data quality
measures, such as counts of admissions and percentages with a primary
22 HSR: Health Services Research 43:1, Part I (February 2008)
diagnosis of R69X (other causes of morbidity and mortality not elsewhere
classified). HES data have improved considerably in recent years and we
believe that they are of great value in performance monitoring if their
drawbacks are taken into account (McKee, Coles and James 1999; Hansell
et al. 2001). Past experience shows that the quality of data improves with use.
Outcome Measures
For diagnosis groups we use death, length of stay, and emergency readmission
to any hospital within 28 days of discharge from the final posttransfer hospital
as outcomes. For the Audit Commission ‘‘basket’’ of procedures that should
Table 1: Case-Mix Variables Used in the Tool
Grouping Method or
Distinct Values Comments
Age 5-year bands Under-1s and those aged 1–4
comprised their own bands
Sex Male, female (other values
Method of
Elective, nonelective
(emergency, transfer from
hospital, maternity event)
Quintile, with an equal
total population in each
Index of Multiple Deprivation
Primary diagnosis Three- or four-character
Used in, e.g., AAA (to detect
presence of rupture), abdominal
hysterectomy (for malignancy),
abdominal GI surgery (for
malignancy, Crohn’s disease
and ulcerative colitis)
Financial year
Month of admission For respiratory diagnosis groups
(easily derived from date of
Palliative care specialty 1 if treatment specialty in
any episode in the
admission coded to
palliative care, 0 otherwise
Charlson index of
Fitted as a factor, capped at 6
Number of emergency
admissions in previous
Fitted as a factor, capped at 3 Requires linking of admissions
to the same patient
AAA, Abdominal Aortic Aneurysm.
National System for Monitoring Clinical Performance 23
mainly be performed as day-case surgery (Audit Commission 2001), the
outcome is the procedure being performed as an inpatient. For other procedure
groups we use death within 30 days of the procedure, length of stay, and
emergency readmission as per the diagnoses. These outcomes are available
from the data and are known to be important. For simplicity, length of stay is
dichotomized into whether or not it exceeds the upper quartile for all patients
nationally, due to the various problems inherent in trying to treat length of stay
as a continuous variable (Yau, Leeb, and Ng 2003). Stays longer than this
admittedly arbitrary cut-off point are deemed to be ‘‘long’’ but are common
enough to enable robust risk estimation.
Use of Statistical Process Control Charts
Instead of aggregating patient outcomes into annual summaries and comparing
each hospital’s outcome rate with the ‘‘expected’’ rate based on the
benchmark (an ‘‘acceptable’’ level of performance, often simply the national
average), individual-level control charts plot patient by patient a function
of the difference between their actual outcome and their expected (a priori)
probability or risk of having that outcome. These charts are run for as long as is
desired in order to have sufficient power to detect a difference between the
observed and expected outcome rates. There are a variety of charts available,
but the log-likelihood cumulative sum (CUSUM) is the most powerful test for
detecting unacceptably high rates for a given false-positive rate (Moustakides
1986). For this and other reasons discussed elsewhere (Marshall et al. 2004) we
have adopted the log-likelihood method of Steiner et al. (2000), which includes
adjustment for the a priori risk according to whatever case-mix variables are
available. This chart requires that the following issues be considered, which
are now discussed: estimation of the expected including case-mix adjustment,
setting of benchmarks and the chart threshold, and what to do when the
threshold is crossed.
Estimation of the Expected Risk of Each Outcome
For each diagnosis or procedure group and outcome, logistic regression models
were constructed using the data for 1996/1997 to 2004/2005. Case-mix
information in HES is limited because the data set was created to measure
activity, but age, sex, method of admission (whether emergency or elective),
quintile of a multiple socioeconomic deprivation score, IMD2004, for the
area (electoral ward) of residence (Office of the Deputy Prime Minister Indices
of Deprivation 2004) and diagnosis or procedure subgroup (e.g., asthma was
24 HSR: Health Services Research 43:1, Part I (February 2008)
divided into asthma and status asthmaticus) were available and were entered
into the model (Table 1). For the respiratory groups, the month of admission
was also included. All patients within the same risk stratum (combination of
age, sex, etc.) were therefore allocated the same risk. The success of case-mix
adjustment for accurately predicting the outcome (discrimination) was evaluated
using the area under the receiver operating characteristic curve (c statistic).
This is between 0.5 (discrimination being no better than chance) and
1 (perfect discrimination); values below 0.7 are considered poor or fair, 0.7–0.8
considered good, and higher values considered very good or excellent.
The area under the curve (c) statistics were generally good or very good
for mortality, but only fair for emergency readmission. In a study comparing
mortality prediction using administrative and clinical data sets, correlations
between hospital-level observed-to-expected ratios ranged for noncardiac
surgery from 0.64 to 0.86 depending on the specialty (Gordon et al. 2005).
Compared with the clinical data sets, the administrative ones identified outlier
hospitals with a sensitivity of 73 percent and a specificity of 89 percent. For
CABG surgery, Geraci et al. (2005) found that administrative data gave a
c statistic of 0.70 compared with 0.76 for the clinical data set, but that adding
just two variables (previous heart surgery and whether the surgery was elective,
urgent or emergency——in English data we distinguish between elective
and emergency admission) increased the c statistic to 0.74. More sophisticated
risk scoring systems have encountered significant problems such as high
complexity and overpredicting risk, and there is some evidence that simple
methods may suffice (Sutton et al. 2002).
Benchmarks and Setting the Chart Threshold
In the absence of agreed benchmarks for our outcome measures, we compare
each trust with the national average. The charts aim to detect twice or over the
national odds for poor performance and half or under the national odds for
good performance. If the patient dies, the chart moves up by an amount
inversely proportional to their a priori risk of death so that the trust is not
unduly penalized when very ill patients die, and moves down if they survive.
The higher the chart rises, the more likely it is that the odds of death for the
trust are twice the national average: a lower threshold gives speedier detection
of high odds but at the cost of a higher false alarm rate. This trade-off between
successful detection and false alarms was assessed by simulation; the emphasis
was on suppressing the false alarm rate because a large number of false alarms
would erode the user’s confidence in the tool. There are other measures of
National System for Monitoring Clinical Performance 25
assessing the statistical performance of the chart beyond the scope of this
article (see, e.g., Frise´n 1992).
When the threshold (‘‘h’’) is crossed, it is immediately reset to a value of
h/2, akin to putting the hospital ‘‘on probation,’’ so that if the hospital’s odds
continued thereafter to be at least twice the national average, this would be
detected more quickly than if the chart had been reset to zero (which would be
akin to ‘‘wiping the slate clean’’). This resetting to h/2 has some theoretical
justification (Lucas and Crosier 1982). An example chart is given in Figure 2,
which shows death from CABG in a sample NHS trust. The OR for the whole
period is 1.44 (95 percent CI 0.95–2.09), not significant at the 5 percent level,
but without the chart, one period of much higher mortality (when the
threshold is crossed) would be concealed.
Further Work
Further improvements to the case-mix model are being evaluated including an
exploration of adjustment for comorbidity using the Charlson index (Sundararajan
et al. 2004). The introduction of payment by Healthcare Resource
Figure 2: Screenshot of Web Front End Showing the Cumulative Sum
(CUSUM) Chart for One Hospital’s Mortality Following Admission for
Coronary Artery Bypass Graft (CABG)
26 HSR: Health Services Research 43:1, Part I (February 2008)
Groups (similar to Diagnosis Related Groups, which use all the diagnosis fields
and not just the primary diagnosis) provides a financial incentive to encourage
the recording of comorbidities, as occurred in the United States (Carter,
Newhouse, and Relles 1990). Also potentially of use are the previous admissions
or surgery within a given time period, which requires the linking of
admissions to the same patient.
We will continue to seek clinical advice in the definitions of procedure
groups and development of relevant outcome measures. Recent English admissions
data also include Intensive Therapy/High Dependency Unit data,
which could be used as a ‘‘near miss’’ outcome instead of or in combination
with death (Steiner, Cook, and Farewell 1999). We dichotomized length of
stay so that an ‘‘event’’ was a stay of more than the upper quartile length of stay
for all patients in order to simplify the analysis. However, such categorization
loses information of course, and, although there are very different approaches
to modeling it as a continuous variable (e.g., Marazzi et al. 1998; Wang, Yau,
and Lee 2002), further work could lead to a fuller understanding of a hospital’s
length of stay distribution.
Although monetary expenditure and clinical performance are very different
in nature, the web-based drill-down flexibility would also suit analyses
of financial flows, and we have a related tool in development that uses current
Healthcare Resource Group tariffs to track financial flows.
In light of a government initiative within the United Kingdomin 2004 to
offer patients elective care appointments from a choice of five hospitals (Department
of Health 2004), we are now working to provide Internet-based
summary analyses using key indicators. This will assist both the patient and
general practitioner in choosing their hospital of treatment.
We have created a systemthat allows themonitoring of clinical outcomes with a
short time lag, with considerable advantages overmore traditional league tables
that are still sometimes used in the United Kingdom or performance rating
systems used previously in health care in England. This system allows for:
! Analysis of timely data, updated monthly rather than annually.
! Use of the most statistically powerful tests for successful, automated
detection of problems at the earliest opportunity (including a quantifiable
screening process for false alarms).
National System for Monitoring Clinical Performance 27
! Interactive front-end capabilities with drill-down options that allow
for enhanced clinical decision making that directly impacts on quality
of patient care and hospital levels of performance.
We envisage the system as a management tool for clinicians and managers,
offering prospective near real-time monitoring of different outcomes
within hospitals. It could act as a focus for intelligently directed clinical audit
with the real potential to reveal both problems and good practice well in
advance of the U.K. Healthcare Commission’s ‘‘annual health check’’ or similar
governmental assessments. The usability of the tool’s front end is important
so that the retrieval of well-presented key information is as quick and easy
as possible. There is some evidence from hospitals such as that given earlier
suggesting that the analyses available within the tool relate to clinical experience
and enhance decision making, but wider availability and prospective
monitoring will be required to fully assess the utility and impact on clinical
practice. Health information technology is increasingly being considered by
state leaders in the United States too to improve health care via public–private
collaboration (Virtual Medical Worlds Monthly 2006).
We are grateful to Joanne Zaborowski at the Capital Health Center in Edmonton,
Canada for her very helpful review of the manuscript and suggestions
for improvement.
Disclosures: The Unit is funded by a grant fromDr. Foster Intelligence (an
independent health service research organization).
Disclaimers: None.
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