South African Psychiatry - February 2019

FEATURE
YEARS LIVED WITH DISABILITY (YLDs)
The GBD studies use the term ‘disability’ to refer to a
loss of optimal health in any of the important health
domains. YLDs quantify functional health loss utilising
the prevalence of a disease or injury state and a
measure of the severity of disability (a disability
weight) caused by that state (i.e. YLD = prevalence
of the disease x disability weight for that disease).
The 1990 GBD study used incidence of disease and
injury but this was changed to prevalence by 2010,
as the use of incidence involved calculations of
prospective average duration of disease. Prevalence
data capture the loss of health at the age at which
it occurs rather than the age at which the disease
is incident.
ADDITIONALLY, PREVALENCE DATA ARE
MORE COMMONLY COLLECTED AT
COUNTRY-LEVEL, AND BETTER ENABLE
ADJUSTMENTS FOR COMMONLY
COMORBID CONDITIONS TO PREVENT
OVERCOUNTING OF DISEASE BURDEN.
THE HIGH COMORBIDITY BETWEEN
DEPRESSION, ANXIETY AND SUBSTANCE
USE DISORDERS IS INCORPORATED BY
COMBINING THE YLDS CALCULATED FOR
EACH OF THE CONDITIONS.
The disability weight is numerical value determined
by using surveys of the general population, where 0
= a state of perfect health, and 1 = a state equivalent
to death (Table IV). It is similar to a Quality Adjusted
Life-Year (QALY), a measure related to loss or gain
of quality of life used by health economists. It
should reflect or quantify the loss of “healthfulness”
caused by the disease or injury. It should not be
a value judgement related to quality of life, the
worth of a person, social undesirability or stigma.
Nevertheless, there is still uncertainty around the
weighting of a disability. For example, substance
dependence, although better defined in the GBD
2015 study to prevent the influence of social values,
may still be affected by perception of disability. It
is possible the more severe weighting for heroin vs
amphetamine dependence may be related to the
distressing withdrawal symptoms reported by heroin
users. However, while amphetamine users may not
perceive their addiction to be so disabling, it may
result in greater psychiatric symptomatology, violent
behaviour, and medical and psychiatric hospital
admissions, which might not be captured in the
disability weight.
Another aspect of the disability weight is the
adaptation by society to that disease state. Hence,
it is possible that where there is a high level of
adaptation to, for example, visual or hearing
impairment, these states may not be as disabling as
in societies which offer little or no assistance to blind
Source: WHO methods and data sources for global burden of disease estimates 2000-2015 1
Table IV Comparison of GBD2010, GBD2015 and revised GHE disability weights.
SOUTH AFRICAN PSYCHIATRY ISSUE 18 2019 * 9