COST UTILITY ANALYSIS

ByJUDY OUMA

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INTRODUCTION CUA relates costs to a single benefit

measure, Benefit measure (utility) is a construct made

up of several benefit categories Benefit categories reflect both quantity and

quality. Quantity of life, expressed in terms of

survival or life expectancy, is a traditional measure that is widely accepted

Quality of life embraces a whole range of different facets of people’s lives, not just their health status.

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INTRODUCTION - INDICATORS

Several indicators developed to adjust mortality to reflect the impact of morbidity or disability

These measures fall into two basic categories, health expectancies health gaps

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INTRODUCTION _ HEALTH EXPECTANCIES measure years of life gained or years of

improved quality of life. disability-adjusted life expectancy

(DALE),healthy adjusted life expectancy

(HALE),quality adjusted life expectancy

(QALE).quality adjusted life years (QALY),

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INTRODUCTION -HEALTH GAPS measure lost years of full health in

comparison with some ‘ideal’ health status or accepted standard. potential years of life lost (PYLL),healthy years of life lost (HYLL),disability adjusted life years (DALY).

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INTRODUCTION – COMMONLY USED UTILITY MEASURES Commonly used benefit measures are QALY

and DALY QALY takes into account both quantity and

the quality of life generated by healthcare interventions. It is the arithmetic product of life expectancy and

a measure of the quality of the remaining life years.

DALY is an indicator of BoD in a population. It takes into account not only premature

mortality, but also disability caused by disease or injury 6

INTRODUCTION – CUA RATIOS

Cost per DALY = total cost divided by DALYs Cost per QALY = total cost divided by QALYs DECISION: selection intervention with lower

(lowest) cost per DALY or cost per QALY

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INTRODUCTION – CUA RATIOS

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INTRODUCTION – WHEN CUA IS APPROPRIATE The problem facing decision maker is:

Which option to be chosen when not sure of impact or level of resources available

Quality of life most important health outcome interventions considered affect both

morbidity and mortality Interventions have a wide range of outcomes

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INTRODUCTION – DATA REQUIREMENTS Cost Data

MOH – direct costs only Societal perspective – all costs (direct, indirect,

intangible) List of inputs (required or consumed), quantify

and valueRetrospective study – actual quantities and values of inputs

Prospective study - quantities and values of needed inputs

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INTRODUCTION – DATA REQUIREMENTS… Effectiveness Data

Best source – randomized control trials (RCT) Studies such cohort, case-control, etc. Published literature Carrying out a study

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UTILITIES

Utility measures are derived from economic and decision theory,

Specifically von Neumann–Morgenstern utility theory, which describes decision making under conditions of risk and uncertainty

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UTILITIES

The objective of the utility measurement process is to determine the score for a specific state of health on the utility scale, which ranges from 0, indicating death, to 1, indicating perfect health.

The utility score an individual assigns to a given health state reflects the desirability or preference that person has for that health state relative to perfect health and death that is, its utility.

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UTILITIES

Utility scores—often referred to simply as utilities—are obtained through specialized measurement techniques: the standard gamble, the rating scale, and the time trade-off.

The distinction between utilities obtained with the standard gamble and values obtained with the rating scale or time trade-off techniques is important.

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QALYS AND CUA

Utility scores provide the weights required to calculate quality-adjusted life years (QALYs) for cost-utility analysis.

In order to measure the output of a medical treatment in QALYs, the health-related quality of life needs to be quantified.

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This generally occurs in two phases. First, patient related research is carried out

that leads to a description of the health states of those who have undergone the treatment in question.

Second, the descriptions of the health states that are at issue in the treatment are valued on an interval scale from 0 to 1.

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In principle, it is possible to determine the quality adjustment factor necessary for calculating QALYs in the patient-related research directly, i.e.: without the interim step of the health states description.

In that case, the patients involved in the research are asked to articulate a valuation of their own health state(s).

This is termed a direct utility assessment. However, this approach is used extremely rarely in

practice. 17

This is because most researchers assume that it is not the actual patient but (a random sample of) the general public that constitutes the most appropriate source of health state valuations in CUAs

Also because clinicians often regard a direct utility assessment as an unacceptable burden on patients

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DOMAIN SPECIFIC INSTRUMENTS

Broadly speaking, four types of measurement instrument can be distinguished.

First of all, there are the domain-specific instruments

These instruments cover one domain of health and can be applied to various diseases.

Examples are the index of independence in Activities of Daily Living (ADL index) and the McGill Pain Questionnaire

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DISEASE SPECIFIC INSTRUMENTS

Then there are the disease-specific instruments.

These instruments are generally developed for medical research to evaluate treatments for one specific disease.

They focus on the dimensions of the concept of health that are affected by the disease at issue.

Examples are the Health Assessment Questionnaire developed for research into people with rheumatic conditions, cancer, e.t.c 20

GENERIC INSTRUMENTS

The third category encompasses the instruments aimed at representing the health concept in general, the general health state instruments.

These psychometric-style instruments are also frequently used in economic evaluation research.

They consist of a large number of questions (‘items’), each representing a particular aspect of the complex concept of health.

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GENERIC INTRUMENTS

The scores in the individual items can be added together to total the most important ‘dimensions’ of health (for example the physical, the psychological

and the social dimensions). These dimensions may in turn, at least with

some instruments, be totalled to achieve a final score for health as a whole.

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GENERIC INSTRUMENTS

These instruments embody both the descriptive and the valuation phase of the research necessary for rating the quality adjustment factor of the QALY.

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GENERIC INSTRUMENTS

Designed to measure the health status of the general population in different socio-economic groups and various cultural settings.

Useful for diverse patient groups independent of the underlying disease or disability.

Widely applicable across various types of diseases, disabilities, impairments, and medical treatments.

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GENERIC INSTRUMENTS

Can be methodologically classified into profile and single index score measures. Profile index score measure describe the health state

from the stand point of various physical and emotional dimensions such as vitality, role limitations caused by emotional difficulties, bodily pain, general health, social function, etc. (as widely used in SF-36 instrument).

single index score measure produces a single index score on a 0–1 scale (some instruments produce also negative scores), which is a necessary requirement for the calculation of QALYs used for a commensurate appraisal of the cost-effectiveness of various health care interventions.

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GENERIC INSTRUMENTS

Generic- single index score instruments include: EQ-5D (EuroQol), Nottingham Health Profile, Sickness Impact Profile Short Form: SF-6D (derived from RAND-36/SF-36), HUI 3 (Health Utilities Index Mark III), The AQoL (Assessment of Quality of Life) and the 15D

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USING THE EQ-5D

Scores for the EQ-5D are generated from the ability of the individual to function in five dimensions. These are:

Mobility 1. No problems walking about. 2. Some problems walking about. 3. Confined to bed. Pain/discomfort 1. No pain or discomfort. 2. Moderate pain or discomfort. 3. Extreme pain or discomfort.

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USING THE EQ-5D

l Self-care 1. No problems with self-care. 2. Some problems washing or dressing. 3. Unable to wash or dress self. Anxiety/depression 1. Not anxious or depressed. 2. Moderately anxious or depressed. 3. Extremely anxious or depressed.

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USING THE EQ-5D… Usual activities (work, study, housework, leisure activities) 1. No problems in performing usual activities. 2. Some problems in performing usual activities. 3. Unable to perform usual activities.

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USING THE EQ-5D…

Each of the five dimensions used has three levels of no problem, some problems and major problems - making a total of 243 possible health states, to which unconscious and dead are added to make 245 in total

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GENERIC INSTRUMENTS Nottingham Health Profile (NHP): Made up 2 parts:

Part 1: Consist of 36 health statement of 6 dimensions: Energy Pain Emotional reaction Sleep, Social isolation, and Physical mobility Part 2: Consist of 7 areas of performance affected by

health: Looking after the home, work, social life, home life, sex,

hobbies, and holidays Questions answered by “Yes” or “No” Widely used Good reliability and validity Limited sensitivity

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GENERIC INSTRUMENTS

Rosser Index: Measures distress and disability through:

8 categories of disability (from no disability to unconscious) and

4 levels of distress (no distress, mild, moderate, severe)

Scores compared to a valuation matrix obtained from 70 respondents from different backgrounds

Quick method

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UTILITY SCORES

Respondents’ self-reported health state is obtained at the start of the McSad interview by presenting themwith a checklist of the items and asking them to identify their level of functioning on each of the dimensions during a specified period preceding the interview, usually seven to ten days

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UTILITY SCORES

The completed checklist is then used to obtain the utility scores using rating scale, TTO or Standard gamble

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EXAMPLE, RATING SCALE

Respondents rank the health states by preference, relative to one another and to the anchor states.

The top anchor of the thermometer, assigned a value of 100, is defined as the most preferred health state (perfect health).

The bottom anchor, assigned a value of 0, is defined as the least preferred health state (death).

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EXAMPLE, RATING SCALE

In this exercise, respondents are asked to imagine living in each of the possible health states without change for the rest of their lives.

They are then asked to place the states of health along the scale in order of preference, spacing them at intervals that reflect the differences in the strength of preference the respondent feels for them.

A utility score between 1 and 0 is computed for each health state.

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EXAMPLE, STANDARD GAMBLE

The standard gamble is presented in the interview as two choices.

Choice A, the uncertain choice, contains two possible health state outcomes, perfect health and death, which have the probabilities of p and 1–p, respectively, of occurring.

Choice B is the certain choice; it includes only one possible health state or outcome, living with HIV virus

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EXAMPLE, STANDARD GAMBLE

Respondents are then asked whether they would prefer to live the remainder of their lives with HIV/AIDs or would prefer a lottery(choice A) in which they would have, say, a probability of .9 of having perfect health for the remainder of their lives and a probability of .1 of immediate death.

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EXAMPLE STANDARD GAMBLE

The probability (p) at this indifference point is the utility score for the health state in choice B.

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MAKING DECISION

Utility scores provide the weights required to calculate quality-adjusted life years (QALYs) for cost-utility analysis.

The following is a simplified example of how they are used.

Utility scores obtained with 15D are .59 for HIV and .32 for AIDs

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MAKING DECISION

For an individual who can be expected to live another 20 years, the QALY figure associated with spending the entire 20 years in the HIV health state would be 6.6 years (20 × .32).

In contrast, the QALY figure associated with spending the entire period in the mild depression health state would be 11.8 years (20 × .59).

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MAKING DECISION

Thus 5.2 quality-adjusted life years are gained as a result of an intervention that moves an individual from the moderate to the mild depression health state.

The cost of treatment per QALY gained is then calculated.

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MAKING DECISION

CUA measures the cost of an intervention compared with the number of QALYs gained by the application of the intervention.

The preferred strategy is the selection of the therapeutic option with the lowest cost per QALY.

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