Alternative approaches to derive disability weights in injuries: do they make a difference?
Juanita A. Haagsma
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S. Polinder
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E. F. van Beeck
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S. Mulder
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G. J. Bonsel
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J. A. Haagsma S. Polinder E. F. van Beeck G. J. Bonsel Department of Public Health, Erasmus Medical Centre, Erasmus University Rotterdam
, Rotterdam,
The Netherlands
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J. A. Haagsma (&) Centre for Infectious Disease Control, National Institute of Public Health and the Environment
, P.O. Box 1, 3720 BA, Bilthoven,
The Netherlands
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J. A. Haagsma G. J. Bonsel Institute for Health Policy and Management, Erasmus Medical Center, Erasmus University Rotterdam
, Rotterdam,
The Netherlands
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S. Mulder Consumer Safety Institute
,
Amsterdam, The Netherlands
Background In burden of disease studies, several approaches are used to assess disability weights, a scaling factor necessary to compute years lived with disability (YLD). The aim of this study was to quantify disability weights for injury consequences with two competing approaches, (a) standard QALY/DALY model (SQM) which derives disability weights from patient survey data and (b) the annual profile model (APM) which derives weights for the same patient data valued by a panel. Methods Disability weights were assessed using (a) EQ5D data from a postal survey among 8,564 injury patients 2 , 5, and 9 months after attending the Emergency Department, and (b) preferences of 143 laymen elicited with the time trade-off method. Results Compared with APM, SQM disability weights were consistently higher. YLD calculated with SQM disability weights was more than three times higher compared with YLD calculated with APM disability weights, for mild injuries with short duration, this increase was six fold. Conclusions The APM seems the preferred method in burden of injury studies that includes mild conditions with a rapid course, since the SQM approach might overestimate the impact of the latter. The APM, however, might underestimate the impact of injury consequences, especially in case of severe injuries.
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Abbreviations
APM Annual profile model
DALY Disability adjusted life years
ED Emergency department
EQ-5D EuroQol-5D
ICD International statistical classification of disease,
Injuries and causes of death
QALY Quality adjusted life years
SQM Standard QALY/DALY model
TTO Time trade-off technique
YLD Years lived with disability
YLL Years of life lost
VAS Visual analogue scale
Since the application of the concept in 1993, the Disability
Adjusted Life Year (DALY) is used increasingly for
priority setting in health care and prevention [1]. The DALY
is a health gap measure that aggregates mortality and
morbidity data, thus allowing comparison of population
health status between countries as well as comparison
between diseases within a country [2]. To aggregate
mortality and morbidity data, years of life lost due to premature
mortality (YLL) and years lived with disability (YLD)
have to be established. Essential for the latter is the
disability weight; a scaling factor that expresses the impact of
a disease with a value ranging from 0, indicating the best
possible health state, through 1, indicating worst possible
health state [3]. By multiplying the disability weight of a
condition by its incidence and its average duration (or
prevalence in case of chronic disease), the healthy time lost
due to living with disability (YLD) is calculated.
Regarding disability weights, there are two dominant
approaches, both have been used in burden of disease
studies. One of these approaches is to adopt existing
disability weights from the Global Burden of Disease study
[4]. In order to compute YLD, the GBD disability weights
are then applied using the standard QALY/DALY model
(SQM). The SQM assumes independence between duration
and disability and it requires that the health state remains
fixed over time [57]. For health states with dynamic and/
or complex patterns this assumption is untenable, since
these health states in fact have to be separated into
numerous parts.
A field abundant of dynamic recovery patterns with a
wide variation in duration is the field of injuries. Moreover,
the existing set of disability weights as published by
Murray et al. [4] lacks a number of highly incident
nonignorable long-term injury consequences, which ultimately
results in an underestimation of the total burden of injury.
To address both the issue of complexity over time and the
issue of incomplete coverage of long-term sequelae,
existing methods have to be adapted or extended. At this
stage, the SQM approach has been administered to several
burden of injury studies [811]. This approach uses a
twostep procedure to assign disability weights to health
outcomes. Firstly, patients report their own health state using
one of the available generic health state classification
systems. These classification systems render the health
state of an individual by the function level that he/she
reports on each of the domains. The weight of that health
state is computed by a formula that firstly yields a partial
weig (...truncated)