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| ii. Quality and quantity |
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Quality as well as quantity
How do we measure the outcome of a medical treatment? Any medical treatment is intended to improve the health status of the patient receiving it. If we take an aspirin to treat a headache, we expect the aspirin to remove the pain and thus make us feel more healthy. This means that measuring health care outputs must involve defining and specifying what we mean by health. In practice, health is usually defined negatively as the absence of illness or disease. However, this ignores the positive aspects of being healthy. The definition of health used by the World Health Organisation (WHO) tries to capture these positive aspects, defining health as:
"A state of complete physical, mental and social well-being, and not merely the absence of disease or infirmity".
This means that we need to include a measure of quality of life when we are evaluating health care outcomes.
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What quality of life?
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Measuring quality of life
For instance, suppose we are trying to evaluate the use of chemotherapy for patients suffering from liver cancer. We are likely to find that the treatment can extend life by a number of months or years. That by itself would suggest that the outcome is beneficial. However, if we also found that there is considerable pain and unpleasant side effects, in other words that the quality of the extra life is very poor, then we may revise our assessment.
So to measure health care output, we need to measure both quantity and quality of life produced. Measuring quantity is fairly straightforward. We can use RCTs to compare how long people live following treatment with how long people with the same illness live who receive either no treatment or a different treatment. So we can measure the output of different treatments in terms of life years saved. Measuring quality of life is much more difficult.
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| Grading states of health
One approach is to construct a table like Table 3 below. We then need to grade the states of health according to how good or bad they are thought to be. Clearly the grading will be subjective (normative) and so will vary from individual to individual.
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Table 3. Grading quality of life relative to perfect health (=1.000).
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None |
Mild |
Moderate |
Severe |
| No disability |
1.000 |
0.995 |
0.990 |
0.967 |
| Slight social disability |
0.990 |
0.986 |
0.973 |
0.932 |
Severe social disability and/or slight impairment of performance at work.
Able to do all housework except very heavy tasks |
0.980 |
0.972 |
0.956 |
0.912 |
Choice of work or performance at work very severely limited.
Housewives and old people able to do light housework only but able to go out shopping |
0.964 |
0.956 |
0.942 |
0.870 |
Unable to undertake any paid employment.
Unable to continue any education.
Old people confined to home except for escorted outings and short walks and unable to do shopping.
Housewives able only to perform a few simple tasks |
0.946 |
0.935 |
0.900 |
0.700 |
| Confined to chair or to wheelchair or able to move around in the house only with support from an assistant |
0.875 |
0.845 |
0.680 |
0.000 |
| Confined to bed |
0.677 |
0.564 |
0.000 |
-1.486 |
| Unconscious |
-1.028 |
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Source : Kind, Rosser and Williams in Jones-Lee,
The value of life and safety, 1982.
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There are a number of different ways in which the grading could be carried out. One is to rank the states of health without any attempt to quantify them - so you simply list the states in order of preference. Another is to try to quantify the utility or disutility involved in each state so that you can say that state 1 is not only better than state 2 but how much better it is. This is technically called a cardinal interval scale. An example of a cardinal interval scale with which we are all familiar is a thermometer. The interval scale has two reference points against which all other states can be compared - the reference points of a Celsius temperature scale are the freezing point and boiling point of fresh water at sea level i.e. 0 degrees C and 100 degrees C. Health measurement scales normally use good health = 1 and death = 0. In the example in Table 3, being confined to bed and in severe pain (distress) is considered to be worse than death.
Look at Questions and Activities for an exercise on measuring quality of life. Now look at the next section on QALYs to see how health economists have tried to create a measure to capture both the quality and quantity elements of a health care outcome.
Now look at these (check the status bar for information)
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What is the link between a thermometer and a scale of health measurement? |
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