ROLE OF ECONOMIC MODELLING IN A COST-EFFECTIVENESS ANALYSIS

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ROLE OF ECONOMIC MODELLING IN A
COST-EFFECTIVENESS ANALYSIS

• Evaluating the cost-effectiveness of
  antimalarials in South Africa
• Charlotte Muheki Zikusooka

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INTRODUCTION

• In a world with limited resources, it is
  necessary to have methods of determining the best
  way to allocate those resources among alternative
  uses.
• Definition Economic Evaluation is a technique
  that was developed by economists to assist
  decision-making when choices have to be made
  between several courses of action.
• There are 4 economic evaluation techniques each
  one involves the systematic identification,
  measurement and valuation of costs and
  consequences / benefits/ outcomes of the
  alternatives under review.

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BACKGROUND SOUTH AFRICA

• Malaria in South Africa in 3 out of 9 provinces
• Development of resistance to antimalarials to
  Chloroquine (CQ) Sulphadoxine-pyremethamine (SP)
• Sky-rocketing malaria cases as a result.
• SP adult dose cost 0.10 compared to AL adult
  dose cost 2.50 (at that time)
• Policy makers need evidence-based information
  showing the effectiveness, costs and
  cost-effectiveness of a range of alternatives, in
  order to make choices.
• Traditional economic evaluation approaches become
  inadequate in situations where the measurement of
  the impact of an intervention is methodologically
  complex.

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MALARIA TRENDS IN KWAZULU-NATAL
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BACKGROUND

• Extended response to the malaria problem,
  including improved vector control (using new
  insecticide for indoor residual spraying) and
  improved management of malaria cases (effective
  antimalarial) and IRS in neighboring districts in
  Mozambique
• Dramatic impact on malaria transmission cases
• To which intervention do attribute the positive
  impact?
• How do conduct a cost-effectiveness analysis in
  this complex situation?
• A range of methods were used, but in this
  presentation we focus on modelling, using the
  decision-tree model

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Economic Modelling

• Modelling a way of representing the complexity
  of the real world in a more simple and
  comprehensible form
• In economic evaluation, modelling is a
  systematic quantitative approach for assessing
  the relative value of one or more decision
  options
• The use of models in cost-effectiveness studies
  has been increasing over the years despite the
  concerns and debates
• Decision-analytic models used in economic
  evaluation include, decision trees, Markov
  models, Monte Carlo (stochastic) simulations, and
  Discrete Event simulations.
• A decision tree graphically depicts components
  of a decision problem and relates actions to
  consequences
• Markov model is a decision-analytic model that
  involves a Markov process, i.e. is a modelling
  technique derived from matrix algebra, which
  describes the transitions a cohort of patients
  make among a number of health states during the
  series of short or long cycles

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MARKOV Model - illustration
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COST-EFFECTIVES OF ANTIMALARIALS IN S. AFR

• Comparing SP and ACTs in 2 provinces (KZN MPM)
• A decision tree was used to evaluate and compare
  the relative impact on costs and health outcomes
  associated with both uncomplicated and severe
  malaria
• SP monotherapy artemether-lumefantrine (in KZN)
• SP monotherapy Artesunate SP (in MPUM)
• Antimalarial effectiveness
• KZN SP (12) AL (99)
• MPUM SP (95) ASSP (99)

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RESULTS FROM DECISION TREE MODEL
KZN Cost Incr Cost Eff Incr Eff C/E Incr C/E
Treat with AL 18.80   0.9999   18.82  
Treat with SP 115.80 97.00 0.9792 -0.0206 118.26 (Dominated)
The strategy "Treat with SP" is dominated by "Treat with AL". The strategy "Treat with SP" is dominated by "Treat with AL". The strategy "Treat with SP" is dominated by "Treat with AL". The strategy "Treat with SP" is dominated by "Treat with AL". The strategy "Treat with SP" is dominated by "Treat with AL". The strategy "Treat with SP" is dominated by "Treat with AL". The strategy "Treat with SP" is dominated by "Treat with AL".
MPUM Cost Incr Cost Eff Incr Eff C/E Incr C/E
Treat with ASP 12.00   0.99987   12.05  
Treat with SP 24.00 12.00 0.99882 -0.00105 24.05 (Dominated)
The strategy "Treat with SP" is dominated by "Treat with ASP". The strategy "Treat with SP" is dominated by "Treat with ASP". The strategy "Treat with SP" is dominated by "Treat with ASP". The strategy "Treat with SP" is dominated by "Treat with ASP". The strategy "Treat with SP" is dominated by "Treat with ASP". The strategy "Treat with SP" is dominated by "Treat with ASP".
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RESULTS

• ACTs were clearly more cost-effective relative
  to SP monotherapy, in both KZN and MPUM.
• Sensitivity analyses of the decision tree model
  consistently confirm that ACTs more
  cost-effective relative to SP monotherapy even
  when the values of different variables are varied
  over a wide range of values.
• C/E ratios were found sensitive to changes in
  some of the variables.
• C/E ratio for the SP option is sensitive to
  changes in the values of pHosp_SP (i.e. the
  probability that a patient who has failed to get
  cured with SP (first time) will seek care at a
  hospital and will be hospitalised to get second
  line treatment).
• The lower the value of pHosp_SP, the lower the
  C/E ratio and vice versa for the SP option.

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KEY FINDINGS AND LESSONS

• Despite being relatively more expensive, ACTs can
  be cost-effective.
• ACTs were not only more cost-effective than SP
  monotherapy, but also resulted in substantial
  cost savings in the Kwazulu Natal and Mpumalanga
  contexts.
• The finding that ACTs are cost-saving in
  Mpumalanga is particularly important in two ways
  
• SP monotherapy was still highly effective in
  Mpumalanga (90) unlike in Kwazulu Natal where
  its effectiveness had declined to only 12
• There had been no changes in local vector control
  programme in Mpumalanga (as was the case in
  Kwazulu Natal)
• Similar findings have been reported by others
  Sudre, P., J.G. Breman, D. McFarland, and J.P.
  Koplan (1992) Wilkins, J.J., N. Valentine, and
  K. Barnes (2002) Institute of Medicine of the
  National Academies (2004) Coleman, P.G., C.
  Morel, S. Shillcutt, C.A. Goodman, and A.J. Mills
  (2004)

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ROLE OF MODELLING IN ECONOMICS

• Health outcomes are normally achievable in the
  very long run
• analysts need to find a method for extending the
  evidence of effectiveness to cover the time
  interval for which effectiveness could logically
  apply
• THUS, the need to use modelling in economic
  evaluation remains of critical importance
• HOWEVER Data needs for economic models are
  normally extensive and such data are not easily
  available, resulting in the need to rely on
  assumptions
• ALSO Limitations with how to present more
  realistic disease epidemiology and health system
  challenges in economic models
• POLICY MAKERS the black-box effect of some
  models makes their results less acceptable by
  policy makers

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FINAL REMARKS

• Economist, epidemiologist, public health
  specialists not trained in economic/mathematical
  models.
• Ability to use modelling techniques in analyses
  either requires prior training on these
  techniques (which is not always feasible) or
  working with specialists in modelling (who
  usually do not have any training in diseases).
• Results of models are not very much trusted and
  accepted by policy-makers and other.
• Use of models in disease modelling and economic
  evaluations is useful and cannot be completely
  avoided.
• How can modelling techniques be improved and made
  more accessible to non-mathematicians?

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THANK YOUfor YOUR ATTENTION