Functional Health Status

In the past, health services were viewed as aiming to save lives and prevent death. However much, perhaps most, of health care is directed toward improving the quality of the patient’s life. General practitioners, specialist psychiatrists, ophthalmologists and otolarynologists, plastic surgeons, obstetricians, physicians in rehabilitative medicine, etc and many other health providers such as podiatrists and physiotherapists spend most of their time attempting to improve the quality of their patients’ lives. Many types of medical procedures are directed primarily at improving a patient’s function whether in a physical, psychological or social capacity.

Health is defined as:

a complete (positive) sense of physical, psychological and social well-being; an ability to function in the community without pain and anxiety, with confidence that care and comfort will be available in times of illness, for a natural life span. (E Price, Supramedicine, 1997)

This definition incorporates not only the absence of disease but the more positive view that patients must be able to perform their social roles at work, in the family and in the community.

So we can conclude that the main reason people attend the doctor is not to prevent dying but to improve living. They attend for a non-functioning sore shoulder, bad back or painful knee. They hope the doctor will be able to improve their health-related quality of life, otherwise known as their “functional health status”.

It has only been in the last 30 years, with the advent of computers, advances in information technology and psychometrics, that this can now be “reliably and validly measured”.

It is noted that any measure of quality of life must to some extent be a “subjective measure”. This term should not be confused with notions of weak or inferior measurement.

There is much evidence that well-constructed subjective measures can be valid and reliable. They measure with a high level of precision what they intend to measure and people can provide stable, replicable, dependable information about subjective phenomena.

Psychometricians have now developed what are known as “multi-dimensional health status profiles”. These are short questionnaires that measure health related quality of life.

The best known of these is the SF-36. Millions of dollars were put into developing and testing this instrument.

The SF-36 measures the following eight health concepts from the client’s point of view.

1. Limitations in physical activities because of health problems
2. Limitations in usual role activities because of physical health problems
3. Bodily pain
4. General health perceptions
5. Vitality – energy / fatigue
6. Limitations in social activities because of physical and emotional problems.
7. Limitations in usual role activities because of emotional problems
8. Mental health (psychological distress and well-being)

Each of these parameters is scored.

These parameters have been found to be valid representations of a person’s health when compared to a broader range of health attributes and when compared to laboratory tests and clinical examination.

The SF-36 is referred to as a generic measure because it assesses health concepts that represent basic human values that are relevant to everyone’s functional status and well-being. Such measures are called generic not only because they are universally valued but also because they are not age, disease or treatment specific. Generic health measures assess health-related quality of life outcomes, namely those known to be most directly affected by disease and treatment.

The SF-36 survey of generic health concepts is a standardised and validated tool for monitoring the results of care, and is used extensively in the USA, Europe and Australia.

Although the current results of the SF-36 cannot be aggregated to produce one score, when each concept is scored out of 100 the eight parameters produce a single histogram or single graph.

The single histogram (graph) has been determined for the normal populations for a large number of countries.

	Graphs adapted from: John E Ware Jr, K K Snow, M Kosinski, B Gandek, SF-36 Health Survey Manual and Interpretation Guide, The Health Institute, New England Medical Centre. Boston, MA, 19934 as presented in: Medical Outcomes Trust Bulletin, Vol 1, Number 1, 1993.

It would be nice and simple if we had one accurate figure, a “personal health index” with “one” only score that summarised an individual’s health status. To date no statistically accurate score has been devised.

The scientist who created or discovered the SF-36 did discover however, on the application of factor-analytic methods, they were able to construct

• Physical Component Summary Measure (PCS)
• Mental Component Summary Measure (MCS)

of health.

The authors assert that these summary health measures provide greater simplicity of statistical analyses.

They also noted that the confidence intervals for SF-36 PCS and MCS scores for individual patients are one half to one fifth the size observed for the SF-36 scales and therefore they may facilitate use of the SF-36 in monitoring individual patients in everyday clinical practice.

Accordingly we now have two separate measures which together are a good representation of health related “quality of life”, or functional health status.

A major aim of all health services is to achieve improvement in these two parameters.

In order to utilise these “patient defined” outcomes in medical decision making the authors of the SF-36 and their summary scales PCS (physical health) and MCS (mental health) realised this was best achieved by utlising norm-based scoring.

A major recalibration using linear transformations was performed so that the average adult in the US was assigned a score of “50” in physical health score, and similarly for the mental health score and all the component scores.

One standard deviation (SD) was assigned a score of 10.

The average well person in the same socio-demography scores “55”.

Having a standard score, in this case “10”, for one standard deviation permits:

• Making comparisons
• Estimating the burden of disease
• Estimating the benefits of treatment

By measuring health outcomes one treatment at a time using the same methodology we have previously used to standardise the norm “health”, we can look at the extent to which a treatment restores someone to his or her usual function.

For example, today’s state-of-the-art treatment for asthma improves physical functioning, as measured by the SF-36, by 0.50SD which raises the score close to what it would be for the average person without asthma.

Using the norm-based scoring of the SF-36 and its physical and mental summary scales, a new hip, a new knee, a new heart, a new heart valve, have been linked to 1 to 1.5 SD average improvement – a huge effect. Similarly, a number of other therapies such as medications for arthritis, for asthma and for migraines are shown to bring a substantial improvement.