Population Health Impact of Disease in Canada (PHI)

Health state descriptions

• Standardized measures of functional limitations
• Defining health states for a disease
• Describing functional limitations associated with health states
• Classifying functional limitations for each health state

Standardized measures of functional limitations

A key challenge of documenting morbidity related to a disease is to provide a standardized measure of severity of functional limitations that result from the disease. These limitations may vary across different types of disease; they may differ depending on how advanced the disease is; they may be affected by treatment for the disease.

It is thus necessary to divide diseases into distinct health states, each with a different profile of functional limitations. For each disease, a comprehensive but manageable set of health states is developed to represent the average or typical experience of Canadians with that disease.

For each health state, a “typical” case is defined, based on a combination of literature review and expert consultation. Although every individual's experience of a given disease will be unique, creating these standard profiles is necessary for measuring health at the population level.

The severity of functional limitation imposed by each health state is established through literature review and expert consultation. Information about pain, physical limitations, emotional state and social capacity are among the information considered.

This information is used to classify the severity of limitation on each of 11 attributes that span physical, mental, and social health. In this way, a large amount of information on the typical experience of a disease is condensed into a more manageable form, which facilitates measurement of the disease's population health impact. To ensure that clinical accuracy is preserved in this process, the health state classifications are reviewed by medical experts and revised accordingly.

The resulting classification for each health state is used to assign a preference score that gives a relative preference for the health state compared with full health. Preference scores contribute to summary measures of population health that quantify the morbidity related to the disease across its various health states and combine it with the impact of mortality.

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Defining health states for a disease

The way in which diseases are divided into various distinct health states depended on the disease: health states can represent different types of disease, various phases in the course or treatment of the disease, or sequelae of the disease. A literature search is conducted to establish this set of health states for each disease. On one hand, the health states need to be reasonably comprehensive in scope; on the other hand, they need to be manageable in number.

Once the health states are identified, a literature review is used to establish the definition of a typical or average case for each health state. Where the literature is not sufficient, expert opinion is obtained to supplement this information. Guidelines have been established to ensure consistency across all diseases being examined in the research program. Three key elements are included in each definition:

1. Clinical or functional definition of the health state,
2. Scope of the health state, including the standard treatment provided in Canada and its side effects, and
3. Average duration of the health state.

PubMed is the primary database used to identify peer-reviewed articles, supplemented by several social science databases: Academic Search Premiere, PsycFIRST, Social Sciences Index, Social Sciences Citation Index, and ERIC. Relevant medical texts and websites of major government and health organizations related to the disease are also consulted.

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Describing the functional limitations associated with the health states

The functional limitations associated with each health state are determined using peer-reviewed literature and medical texts, then reviewed by a clinical expert or medical panel. Information about symptoms and other effects is gathered so that health states can be classified using the 11 attributes of the Classification and Measurement System of Functional Health (CLAMES). Particular emphasis is placed on distinguishing the level of severity for functional limitations.

The descriptions encompass functional limitations related to the health state and include the effects of standard care available to Canadians. If management of pain or other symptoms is generally successful, these effects are included, as are major side effects of treatment.

Standardized templates are used to record and synthesize the information provided by the literature review. For each health state, an Excel workbook with a series of worksheets is prepared. These workbooks are established to organize the evidence and sources from which it is obtained in a consistent fashion across health states. This is particularly important to maintain consistency and structure with the other diseases being reviewed in a similar way for this research program.

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Classifying functional limitations for each health state

The functional limitations related to each health state are classified using CLAMES. Numeric codes for the level on each attribute are entered into the structured spreadsheets along with the symptoms and other information used to support this classification.

Preliminary decisions on classification levels are made by research assistants, and then reviewed by the project manager and clinical expert or medical panel with the help of the evidence provided in the spreadsheets.

Functional limitations are classified by the severity of functional limitation rather than by specific symptoms. Symptoms or other descriptions are thus mapped onto generic descriptors of functional limitations. Descriptors used to classify cancers are provided as an example (Table 1).

Monograph chapters are being prepared to document the classification of health states. Figure 1 provides a sample definition, description, and classification. The first sentence defines the scope of the health state. The remaining text provides the description of symptoms and other information used to classify the severity of functional limitations.

Figure 1 Description and classification for a health state related to cancer

Remission after surgery
Description	This description includes the long-term effects of having had surgery only, not in combination with any other therapy. Fatigue, insufficient sleep and insomnia are reported following surgery. Patients requiring radical surgery frequently report severely restricted social and sexual activities. Breast cancer patients experience numbness, pain and swelling in the affected arm; lung cancer patients complain of dyspnea; those having surgery for colorectal or prostate cancer can experience persistent bowel and/or bladder problems. Anxiety and psychological distress can result from follow-up visits.
Classification	PD	PF	ES	FA	MT	SR	AN	SP	HE	VI	HF
	2	2	2	2	1	3	2	1	1	1	1

The classification is represented as a series of numbers to make it easier to compare across health states. Eleven attributes are presented in two groups: core attributes that were expected to apply most broadly to health states representing various phases of the major disease groups, and supplementary attributes that were expected to be less commonly observed.

How to read the classification

A statistical function is used to transform the classification into a preference score.

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Table 1 Descriptors used to classify health states related to cancers

Attribute	Level 2	Level 3	Level 4
Pain or Discomfort	Epigastric pain Mouth sores Sore throat Sore muscles Headache Fever Cough Dyspnea Bladder, bowel irritation Diarrhea Constipation Nausea Vomiting	Inadequate pain management Acute reaction of skin Skin ulcers	Severe pain
Physical Functioning	Muscle weakness Bowel or bladder obstruction Bowel or urinary incontinence Urinary control problems Edema Neuropathy Reduction in muscle mass Decreased stamina Limited arm movement Arm weakness Weakness in legs Unstable gait Parasthesia of feet Dizziness Limitations of activities	Drains and incisions Temporary colostomy, catheter Interference with usual roles	Can no longer fulfil usual roles
Emotional State	Depression	Depression Depressive symptoms Emotional distress Emotional effects of realizing disease or mortality Emotional effects of hormonal therapy *	Major depression High risk of suicide Sadness, grief Psychological distress
Fatigue	Fatigue, some fatigue Insufficient sleep Insomnia	Total lack of energy Chronic fatigue Lethargy Post operative fatigue	Severe fatigue Persistent sense of tiredness Unlikely to be relieved by rest
Memory and Thinking	Confusion Difficulty concentrating Problems with memory and attention Amnesia		Mental clouding and confusion Impairment in cognitive functioning Impaired perception and thinking Poor memory and problem solving
Social Relationships	Relationship stress/issues Employment/marital problems Family disturbances Some disruption of social relationships* Loss of self esteem Body image issues Impotence Reduced/decreased sex drive Sexual dysfunction	Social isolation Restricted social and sexual activities Behavioural changes Mood swings Hospital stay Effect of poor prognosis on relationships*	Distancing themselves * Don't want to see people or go out *
Anxiety	Distress Fear of future/recurrence	Worry, anxiety Daily concern/fear about impending death Worry about recurrence and treatments* Anxiety related to unrelieved pain Worry about family Stress response to surgery* Response to diagnosis*	High levels of stress Hopelessness
Use of Hands and Fingers	Paresthesia in hands

Notes:

1. Emotional State , Memory and Thinking, Social Relationships, and Use of Hands and Fingers each have five levels. Level 1 indicates that there are no limitations for this attribute.
2. For health states related to cancer, there were no limitations on three attributes, Speech, Vision, and Hearing.
3. All terms are from the literature except those marked with an asterisk (*), which were derived from clinical experience.
4. Clinical expertise was also required in some cases to distinguish between levels, e.g. for fatigue and depression.

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