Quality of life is defined as an individuals perception of their position in life in the context of the culture and value systems in which they live and in relation to their goals, expectations, standards and concern. It is a broad ranging concept affected in a complex way by the persons physical health, psychological state, level of independence, social relationships, and their relationships to salient features of their environment1. Since health is the most valued state2,3 health status is being increasingly referred to as Health Related- Quality of life ( HR- QOL ).
Health related Quality of life (HR- QOL) is patient based and multidimensional. There is an observation that the doctors and patients perception of outcome are significantly different4,5,6. There is ongoing debate about assessment of quality of life as a distinction between objective and subjective data7. Objective data are externally observable and directly measurable along a physical dimension. but focuses more on the impact of a perceived health state on the ability to live a fulfilling life. Quality of life may be viewed in terms of an individual, group, or large population of patients. The World Health Organisation's definition of health is 'a state of complete physical, mental and social well- being and not merely the absence of disease or infirmity'.
In order to understand the principles of health measurement, one has to think of the human being as a measuring instrument. The work of psychophysicists8 has developed on judgements made on measurable physical stimuli (e.g. length, weight, loudness). These are as equally relevant to judgements about health as it is to judgements about physical stimuli.
One of the important concept of health outcomes in neurosurgery is the postoperative course as a direct result of our interventions. We may not realise, but the simple 'how are you?' or 'have you any pain?' are the basic tenets of measuring outcome in the outpatient clinic. The traditional measures to assess outcome in neuro oncological surgery are the extent of surgery, postoperative surgical neurological examination and in hospital morbidity and mortality. The next step in the journey of a patient with a brain tumour may involve radiotherapy and chemotherapy. One has to take into account the toxicity associated with this treatment and its influence on the quality of life. The patient with head injury on the one hand may have severe impairment but may also be able to function with mild or moderate neuropsychological sequelae. In a similar fashion, patients with spinal injuries may have neurological deficit but also devastating psychological consequences. There are a number of reasons to rigorously measure outcome in neurosurgery. Firstly, due to technological advancements as well as the spiralling cost of health care we are being held accountable, hence required to demonstrate the benefit of our interventions and the relative benefit of different interventions. One of the other factors is the extraordinary publicity given to relatively infrequent medical scandals.
In neurosurgery, the Glasgow Outcome Score9 and the Karnofsky Performance Index10 are mainly used to measure outcome. Two limitations of single item, traditional measures have been highlighted i.e. they provide little information about the diverse consequence of disease and they fail to incorporate the patient perspective11. Although, single item measures are simple, user friendly and appropriate for measuring some individual properties they have a number of scientific limitations. Single item measures are likely to be interpreted in different ways by different -observers, may not discriminate fine degrees of an attribute and may be unreliable as they do not produce consistent answers over time. Finally, the measurement properties of single item measures are difficult to estimate.
In neurosurgery, the Glasgow Outcome Scale (GOS) is the most widely used outcome measure after traumatic brain injury and other neurosurgical conditions, but it is increasingly recognized to have important limitations. The main criticism of the GOS is that the categories are too broad and do not allow discrimination of important clinical change. However, it is universally accepted and can be easily administered. The Karnofsky Performance Index is also used to measure outcome particularly in neurooncology. It is not designed as a quality of life measure, but is frequently used as such. It was originally designed for use with lung cancer patients, but has also been used for breast cancer. The Karnofsky scale measures physical dimensions of life, rather than social and psychological dimensions. The results for construct and concurrent validity are generally good12. Various studies have reported poor inter- rater agreement13. A major disadvantage of the Karnofsky scale is that it involves categorization of patients by another person.
Multi-item instruments, where each item addresses a different aspect of the same underlying construct are able to overcome the scientific limitations of single items. More items increase the scope of the measure, are less open to variable interpretation, enable better precision and improve reliability by allowing random errors of measurement to average out14.
One of the difficulties in multi-dimensional measurement is to determine if the generic measures are adequate to measure outcome or if there is a need to develop more disease specific measures. In neurological disease, a combination of generic and disease specific questionnaires have been used quite effectively to determine outcome.
Developing And Evaluating Rating Scales
A. Development of Scales
Before embarking on the development of a new instrument, one should define exactly what the instrument is to measure. This is similar to writing a protocol for a clinical study. In order to specify measurement goals, a clear strategy will help other users of the instrument to recognise its use in their own patients.
For example, the patient population should be defined with patient characteristics, inclusion/ exclusion criteria, and other factors that may influe