National Burden of Disease, Injuries and Risk Factors Study in Scotland
Oscar Mesalles-Naranjo
Senior Information Analyst
o.mesalles-naranjo@nhs.net
Burden of Disease Methodological Workshop, 15-16th September 2016
Royal Society of Edinburgh, Scotland
National Burden of Disease, Injuries
and Risk Factors Study in Scotland
Key parameters
Background
•
Scottish Burden of Disease (SBoD) study uses the GBD 2013
study methods applied to Scottish electronic health records.
•
We do minimal changes to the main parameters of the
methodology and only when there’s evidence that this is
necessary.
•
The main parameters of the methodology are:
-
Disease list definitions;
-
International Classification of Diseases (ICD) mappings to
disease list and ill-defined deaths (IDD) groups;
-
IDD and its distribution;
-
Health states and associated disability weights;
-
Mappings of health states to disease list;
-
Severity distribution of disease prevalence;
-
Disease models.
2/19
Ill-defined deaths (IDD)
•
Definition
•
Redistribution process
•
Methods to calculate the redistribution
parameters
3/19
Ill-defined deaths (IDD): definition
•
IDD are defined in opposition to cause specific deaths (CSD).
•
CSD are deaths recorded with a disease or injury which initiated
the train of morbid events leading to death.
•
IDD are usually coded using ICD codes that signify signs,
symptoms and conditions, or intermediate or immediate cause
of death.
•
Although we have a clear definition of what an IDD is, a national
burden of disease project may change which ICD codes belong
to that category.
4/19
Ill-defined deaths (IDD): redistribution process
•
To accurate account for the burden of mortality IDD are
redistributed to CSD.
•
This redistribution is done by classifying IDD into groups, and
defining the CSD target groups where the IDD group contributes
to.
Adapted from Global Burden of Disease study 2010, Web Table 4a
5/19
α
+
β
+
γ
= 1
Ill-defined deaths (IDD): redistribution methods
•
Different methods to allocate IDD to CSD:
1.
Fixed proportions;
2.
Proportionate allocation;
3.
GBD 2013 study, Ahern et al. Population Health Metrics
2011.
•
In Scotland, we record up to ten secondary causes of death.
There’s scope to use this information to either classify a IDD as
a CSD or to define country-specific distribution of IDD.
•
However, in the Scottish Burden of Disease study we use GBD
2013 distribution matrix and apply either fixed or proportionate
allocation, by age and sex.
6/19
Ill-defined deaths (IDD): redistribution methods
•
Ahern et al, 2011: a linear regression where the outcome is the
% of cause-specific deaths and the covariates are the % of each
ill-defined death target group:
[% of CSD group
A
] =
β
A1
[% of IDD group
1
] +
β
A2
[% of IDD group
2
] + ... +
α
A
•
Example for only one covariate
%CSD
target group A
versus %IDD
group 1
for a specific year, age group and
gender.
7/19
Disability weights (DW)
•
Role of health states (HS) and methods to
obtain disability weights (DW)
•
What options are available for a national
burden of diseases study?
•
Criticisms to disability weights
•
DW in the SBoD study
8/19
Disability weights (DW): methods
1.
Define a list of health state (HS) description
They should be able to cover the health effects of all the conditions in
the disease list.
2.
Who is going to compare each HS and how they are going to
compare it.
3.
Translate the results into a positive number lower than 1.
4.
Assign disease DW based on the HS disability weights.
9/19
Disability weights (DW): methods
1.
Define a list of health state (HS) description:
•
could be disease specific or generic applying to multiple diseases;
•
consider or ignore how long the health state lasts.
2.
Who is going to compare each HS:
•
patients ;
•
general population surveys ;
•
medical experts;
and how they are going to compare it:
•
pair-wise comparison,
•
person trade-off;
10/19
Disability weights (DW): options
•
What’s the best option regarding DW for a national burden of
disease study?
•
Build its own
•
Use an existing one and modify it accordingly
•
Use one off the shelf, let’s say GBD study.
11/19
Disability weights (DW): criticisms
•
GBD 2010
disability weights were subject to criticism:
Some DW don’t make sense when making pairwise comparison
or when looking at them individually. For instance in GBD 2010
cannabis dependence=0.33 VS profound intellectual disability=0.16
deafness=0.03
spinal cord lesion below neck: treated = 0.05
•
Explanations:
incompetence of survey respondents;
incompleteness or inaccuracy of HS description
addition of social implications for some HS but not others
•
GBD 2013
appeases some of the criticism:
cannabis dependence=0.27 (0.178, 0.364) VS PFI=0.2 (0.133, 0.283)
deafness=0.22 (0.134, 0.288)
spinal cord lesion below neck: treated = 0.30 (0.198 , 0.414)
•
The DW confidence interval allows defining a
confidence
interval in YLD
and do a
sensitivity analysis
on the ranking of
the diseases, if you wish.
12/19
Disability weights (DW) in SBoD
•
We use GBD 2013 disability weights in the Scottish Burden of
Disease.
•
Some manual work required to match the description of the
disease sequelae and the health states to obtain the disease
sequelae disability weight.
•
We combine health state using a multiplicative model:
DW = 1 – (1 – DW
hs1
)*(1 – DW
hs2
)*...
13/19
From GBD 2013 study
Disability weights (DW) in SBoD
•
HS in most cases describe increasing severity level of disease:
•
Which suggest we could use primary care or secondary care
data to extract prevalence of each severity level.
•
However, we don’t take this approach but rely in worldwide
severity distributions.
14/19
Severity distributions (DW)
•
Definition
•
Worldwide SD
•
Adapting SD to SBoD
15/19
Severity distributions (SD): definition
•
The term ‘severity distribution’ is used to describe the distribution
of prevalent cases of a condition across all its constituent HS,
whether sequelae or severity levels.
•
These SD come from GBD published data:
-
Disease specific papers (MSK disorders, mental disorders...), or;
-
Estimating the distributions of health state severity for the GBD
study, Bursein et al. Population health Metrics (2015)
•
We fill the gaps with worldwide prevalence data published at
sequelae level:
16/19
Severity distributions (SD): worldwide SD
•
Worldwide severity distribution is hardly applicable to any
country. We use it as starting point to engage with medical
community.
•
SD is a challenging aspect of the Scottish Burden of Disease, as
health data doesn’t contain that level of detail, with some
exceptions: chronic kidney disease, depression, asthma, mild
COPD... In the future, we plan to develop SD estimates for some
diseases based on health data.
•
Nevertheless, for any chronic disease we could estimate the %
of
asymptomatic cases
by:
•
But we still need much more information than only the
asymptomatic cases.
17/19
Severity distributions (SD) in SBoD
•
The severity level/sequelae in GBD study conceals much more
detail than just mild, moderate and severe cases of the disease.
There are 25 sequelae for pneumococcal meningitis (PM), for
instance:
•
While worldwide SD may not be applicable to Scotland, we lack
the evidence to replace them for others.
•
We modify the worldwide SD,
redistributing
the
asymptomatic
severity level when the disease is mainly causing
short term
outcomes
, because patients using the health system are not
asymptomatic.
18/19
Questions and Discussion
•
Disease list definitions;
•
International Classification of Diseases (ICD) mappings to
disease list and ill-defined deaths (IDD) groups;
•
IDD and its distribution;
•
Health states and the associated disability weights;
•
Mappings of health states to disease list;
•
Severity distribution of disease prevalence;
•
Disease models.
Key parameters
20
“The asymptomatic category represents not only the
percentage of individuals with disease and no symptoms but,
[...], can also capture the fluctuation in and out of symptoms
over time in the population with the condition. [...]
In other words, some proportion of individuals with diagnosed
anxiety in the past year would not be symptomatic at the time
of the survey”.
Burstein et al. Population Health Metrics 2015
The Scottish Burden of Disease Study utilizes GBD 2013 methods on electronic health records with minimal changes. Key parameters include disease list definitions, ICD mappings, disability weights, and disease models. Learn about Ill-defined deaths (IDD) definition and redistribution process.
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Scottish Public Health Observatory logo National Burden of Disease, Injuries and Risk Factors Study in Scotland Key parameters Oscar Mesalles-Naranjo Senior Information Analyst o.mesalles-naranjo@nhs.net Burden of Disease Methodological Workshop, 15-16th September 2016 Royal Society of Edinburgh, Scotland
Background Scottish Burden of Disease (SBoD) study uses the GBD 2013 study methods applied to Scottish electronic health records. We do minimal changes to the main parameters of the methodology and only when there s evidence that this is necessary. The main parameters of the methodology are: - Disease list definitions; - International Classification of Diseases (ICD) mappings to disease list and ill-defined deaths (IDD) groups; - IDD and its distribution; - Health states and associated disability weights; - Mappings of health states to disease list; - Severity distribution of disease prevalence; - Disease models. 2/19
Ill-defined deaths (IDD) Definition Redistribution process Methods to calculate the redistribution parameters 3/19
Ill-defined deaths (IDD): definition IDD are defined in opposition to cause specific deaths (CSD). CSD are deaths recorded with a disease or injury which initiated the train of morbid events leading to death. IDD are usually coded using ICD codes that signify signs, symptoms and conditions, or intermediate or immediate cause of death. Although we have a clear definition of what an IDD is, a national burden of disease project may change which ICD codes belong to that category. 4/19
Ill-defined deaths (IDD): redistribution process To accurate account for the burden of mortality IDD are redistributed to CSD. This redistribution is done by classifying IDD into groups, and defining the CSD target groups where the IDD group contributes to. CSD targets Chronic Kidney Disease Ischemic heart disease X - Maternal haemorrhage - X Cerevebrovascular disease X - IDD group Hypertension Pulmonary embolism Abortion X X Neoplasms X - Cardiomiopathy - X Injuries - X X - ... Adapted from Global Burden of Disease study 2010, Web Table 4a CSD targetB count + Underlying cause of death for a death record IDD or CSD Redistribution of IDD IDD group CSD targetC count + CSD targetA count + CSD targetAcount + 1 + + = 1 5/19
Ill-defined deaths (IDD): redistribution methods Different methods to allocate IDD to CSD: 1. Fixed proportions; 2. Proportionate allocation; 3. GBD 2013 study, Ahern et al. Population Health Metrics 2011. In Scotland, we record up to ten secondary causes of death. There s scope to use this information to either classify a IDD as a CSD or to define country-specific distribution of IDD. However, in the Scottish Burden of Disease study we use GBD 2013 distribution matrix and apply either fixed or proportionate allocation, by age and sex. 6/19
Ill-defined deaths (IDD): redistribution methods Ahern et al, 2011: a linear regression where the outcome is the % of cause-specific deaths and the covariates are the % of each ill-defined death target group: [% of CSD groupA] = A1 [% of IDD group1] + A2 [% of IDD group2] + ... + A Example for only one covariate 3.0% % CSD target group A, year YYYY, age Country USA Italy Germany UK Canada Mexico Switzerland %CSD 0.015 0.028 0.014 0.014 0.016 0.024 0.005 %IDD 0.05 0.057 0.03 0.04 0.065 0.075 0.02 Italy 2.5% Mexico 2.0% group and sex Canada Germany USA 1.5% UK 1.0% %CSD target group A versus %IDD group 1 for a specific year, age group and gender. 0.5% Switzerland 0.0% 0.0% 2.0% 4.0% 6.0% 8.0% 10.0% % IDD group 1, year YYYY, age group and sex 7/19
Disability weights (DW) Role of health states (HS) and methods to obtain disability weights (DW) What options are available for a national burden of diseases study? Criticisms to disability weights DW in the SBoD study 8/19
Disability weights (DW): methods Adapted from Haagsma et al. Population Health Metrics 2014, 12:20 1. Define a list of health state (HS) description They should be able to cover the health effects of all the conditions in the disease list. Who is going to compare each HS and how they are going to compare it. Translate the results into a positive number lower than 1. Assign disease DW based on the HS disability weights. 2. 3. 4. 9/19
Disability weights (DW): methods Adapted from Haagsma et al. Population Health Metrics 2014, 12:20 1. Define a list of health state (HS) description: could be disease specific or generic applying to multiple diseases; consider or ignore how long the health state lasts. Who is going to compare each HS: patients ; general population surveys ; medical experts; and how they are going to compare it: pair-wise comparison, person trade-off; 2. 10/19
Disability weights (DW): options What s the best option regarding DW for a national burden of disease study? Build its own Time consuming No international benchmark Gain national credibility and improve consistency with national perceptions of HS Use an existing one and modify it accordingly Still time consuming Policy makers may introduce bias Improve consistency with national perceptions of HS Use one off the shelf, let s say GBD study. Reliance on an external organisation HS are irrelevant or the disability weight associated doesn t reflect the reality of the country International benchmark More resources for estimating other key inputs 11/19
Disability weights (DW): criticisms GBD 2010 disability weights were subject to criticism: Some DW don t make sense when making pairwise comparison or when looking at them individually. For instance in GBD 2010 cannabis dependence=0.33 VS profound intellectual disability=0.16 deafness=0.03 spinal cord lesion below neck: treated = 0.05 Explanations: incompetence of survey respondents; incompleteness or inaccuracy of HS description addition of social implications for some HS but not others GBD 2013 appeases some of the criticism: cannabis dependence=0.27 (0.178, 0.364) VS PFI=0.2 (0.133, 0.283) deafness=0.22 (0.134, 0.288) spinal cord lesion below neck: treated = 0.30 (0.198 , 0.414) The DW confidence interval allows defining a confidence interval in YLD and do a sensitivity analysis on the ranking of the diseases, if you wish. 12/19
Disability weights (DW) in SBoD We use GBD 2013 disability weights in the Scottish Burden of Disease. Some manual work required to match the description of the disease sequelae and the health states to obtain the disease sequelae disability weight. From GBD 2013 study We combine health state using a multiplicative model: DW = 1 (1 DWhs1)*(1 DWhs2)*... 13/19
Disability weights (DW) in SBoD HS in most cases describe increasing severity level of disease: Dementia, mild has some trouble remembering recent events, and finds it hard to concentrate and make decisions and plans. Dementia, moderate Dementia, severe has memory problems and confusion, feels disoriented, at times hears voices that are not real, and needs help with some daily activities. has complete memory loss; no longer recognizes close family members; and requires help with all daily activities. Which suggest we could use primary care or secondary care data to extract prevalence of each severity level. However, we don t take this approach but rely in worldwide severity distributions. 14/19
Severity distributions (DW) Definition Worldwide SD Adapting SD to SBoD 15/19
Severity distributions (SD): definition The term severity distribution is used to describe the distribution of prevalent cases of a condition across all its constituent HS, whether sequelae or severity levels. These SD come from GBD published data: - Disease specific papers (MSK disorders, mental disorders...), or; - Estimating the distributions of health state severity for the GBD study, Bursein et al. Population health Metrics (2015) We fill the gaps with worldwide prevalence data published at sequelae level: World wide prevalence Severity distribution (%) Disease severity level/sequelae Maternal hemorrhage (< 1L blood lost) Maternal hemorrhage (> 1L blood lost) Mild anemia due to maternal hemorrhage Moderate anemia due to maternal hemorrhage Severe anemia due to maternal hemorrhage Total 146.6 25.7 7 1 1,097.70 54 36 2 100 723 34.3 2,027.40 16/19
Severity distributions (SD): worldwide SD Worldwide severity distribution is hardly applicable to any country. We use it as starting point to engage with medical community. SD is a challenging aspect of the Scottish Burden of Disease, as health data doesn t contain that level of detail, with some exceptions: chronic kidney disease, depression, asthma, mild COPD... In the future, we plan to develop SD estimates for some diseases based on health data. Nevertheless, for any chronic disease we could estimate the % of asymptomatic cases by: active patients in the period =100 * (1 ) % of asymptomatic patients total patients year But we still need much more information than only the asymptomatic cases. 17/19
Severity distributions (SD) in SBoD The severity level/sequelae in GBD study conceals much more detail than just mild, moderate and severe cases of the disease. There are 25 sequelae for pneumococcal meningitis (PM), for instance: Borderline intellectual disability due to PM Severe motor plus cognitive impairments due to PM Epilepsy due to PM Blindness due to PM Mild hearing loss with ringing due to PM 10% 5% 2% 2% 2% While worldwide SD may not be applicable to Scotland, we lack the evidence to replace them for others. We modify the worldwide SD, redistributing the asymptomatic severity level when the disease is mainly causing short term outcomes, because patients using the health system are not asymptomatic. 18/19
Scottish Public Health Observatory logo Questions and Discussion Disease list definitions; International Classification of Diseases (ICD) mappings to disease list and ill-defined deaths (IDD) groups; IDD and its distribution; Health states and the associated disability weights; Mappings of health states to disease list; Severity distribution of disease prevalence; Disease models. Key parameters
The asymptomatic category represents not only the percentage of individuals with disease and no symptoms but, [...], can also capture the fluctuation in and out of symptoms over time in the population with the condition. [...] In other words, some proportion of individuals with diagnosed anxiety in the past year would not be symptomatic at the time of the survey . Burstein et al. Population Health Metrics 2015 20
