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Epidemiological Methods in Studies of Symptoms in Advanced Disease
Author Bios
Why Study Advanced Disease?
Why Epidemiology?
Incidence and Prevalence
Using Incidence and Prevalence
Definition of a Case
Defining Time, Place, Person
Types of Study Design
Cross-Sectional Studies
Longitudinal Studies
Measurement
Bias
Selection Bias
Measurement Bias
Presenting and Interpreting Results
Currently selected selection: Practical Example
Calculating Prevalence
Conclusion


Chapter 19: Epidemiological Methods in Studies of Symptoms in Advanced Disease: Practical Example: Using Epidemiological Information to Estimate Need for Health Care Services
        

The NHS Executive guidance on the needs assessment of palliative care groups those conditions requiring palliative care as follows:

  1. Progressive cancers. The main categories are cancers of lung, trachea, bronchus, gastro-intestinal, genito-urinary, female breast, ear, nose and throat, lymphatic, leukaemia and haemopoetic, brain and other cancers, including those which present with metastasis and where the primary cancer is not known.
  2. Progressive non-malignant diseases, which can have a palliative period. These include diseases of the circulatory system (most commonly heart diseases, such as chronic heart failure, and cerebrovascular diseases, such as stroke); diseases of the respiratory system (most commonly chronic obstructive pulmonary disease), diseases of the nervous system and sense organs (most commonly motor neurone disease, multiple sclerosis, ALS), dementia, and AIDS/HIV.
  3. Children's terminal illnesses, and hereditary diseases, including degenerative disorders such as muscular dystrophy and cystic fibrosis. (This last group is beyond the scope of this report and needs separate consideration.)

This would be a sensible way to group the data.

If you are unable to get information on the actual number of deaths, the Health Care Needs Assessment for Palliative and Terminal Care provides information on the average number of cancer and non cancer deaths per million population in developed populations. Generally speaking, for every 100,000 people in a population with the same age and gender distribution as the UK, there will be 1,000 deaths per year. Of these around 1 in 4 will be from cancer. The actual numbers of deaths will of course depend on the age distribution of the population (there are more deaths among older age groups), and other local factors.

Each disease would have roughly three groups of patients:

  • Those who had a palliative period of advancing, progressive disease;
  • Those who had stable or no disease, relatively few symptoms but then deteriorate or die suddenly (e.g. from a myocardial infarct); and
  • Those who suffered from chronic disease, where the disease was not clearly progressing, but who might have periods of progression and symptoms where they would benefit from palliative care, and then periods of remission.

Once the numbers of deaths is obtained it is then possible to begin to estimate the numbers of patients who will die, and therefore require end of life and palliative care. Among cancer patients the period of progression is most clearly predicted and many would fall into category (1). However, the other conditions, such as circulatory disease, would include patients in all three categories. Patients may change from one category to another, and spend different periods in each category, and thus with different needs.

The natural history of different non-cancer conditions towards the end of life is only now beginning to be better researched. For example, stroke is a major cause of death with a mortality rate of 30% that may be as high as 60% among patients with severe strokes. The causes of mortality include cerebral edema and herniation, co-morbidity, infection, and other stroke related complications despite active medical intervention. Death in most stroke patients is not sudden but occurs a few days to a few weeks after the acute episode. 20% of people who suffer a stroke die within the first month.

Note also that for some conditions, such as neurological conditions like ALS (motor neuron disease), the trajectory of illness is longer than that of many common cancers, such as lung cancer. Thus patients with slowly progressive conditions may need care for longer than cancer patients. This demonstrates the importance of distinguishing incidence (indicated here by number of deaths) from prevalence (frequency of problems).

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