Measures of Health Status

Measures of Health Status

·        No single or ideal way of measuring a person‟s or a population‟s health status ® wide range of tools

·        Purposes of measuring health status:

o   Diagnostic: to discriminate between people with different health states

o   Prognostic: to predict future events

o   Evaluative: eg before and after a health intervention

·        Measuring health status of individuals and populations:

Mortality

·        Definitions:

o   Crude Mortality Rate: number of deaths per year for an entire population 

o   Specific Mortality Rate: Number of deaths occurring within a subgroup of the population. Eg age, sex, or cause specific 

o   Age adjusted mortality rate: adjusts with reference to a standard population to allow comparisons between populations with different age distributions

o   Premature mortality: death occurring before the average life expectancy within a given population

·        Advantages:

o   Death is easy to diagnose

o   Is recorded, and doctors are legally bound to state the cause

·        Disadvantages:

o   Cause not always accurately described

o   Reduces health status to being alive or not.  Ignores the continuum of suffering and unhappiness

Life Expectancy

·        = The expectation for life at birth for a population born in a specific year

·        Calculation: 

o   Period life expectancies: average life-time of a hypothetical group born in a specific year, assumes age and sex specific death rates won‟t change

o   Cohort life expectancy: follow through a real cohort until all are dead

·        Making comparisons, eg between Australia and NZ:

o   Migration between the two countries

o   Ethnic groups (Maori, Pacific Islanders, Aborigines)

o   Socio-economic differences

·        Potential years of life lost (PYLLs): potential years of life lost for a specific cause. Difference between age of death and the life expectancy at that age

·        Changes over time have largely been due to social and economic changes (particularly public and personal hygiene). Contribution from health services is much less important

Morbidity

·        Incidence or prevalence of a condition or disease in a population over a set period of time

·        Measurement:

o   „Objective‟ measures:

§  Biochemical markers (eg blood glucose)

§  Physiological markers (eg blood pressure)

§  Pathological markers (eg tumour size)

o   Functional measures: 

§  Impairment: reduction in physical or mental capacity – usually due to an organ/system. May be able to be corrected (eg reading glasses)

§  Disability: restriction in a person‟s ability to perform a certain task (eg walking)

§  Handicap: If disability limits ability to perform a normal role – depends on social context

§  Many measures assess degree to which people can undertake activities of daily living

·        Sources of morbidity data: cancer registers, notifications (infectious diseases, workplace accidents), hospital discharges, GP registers

·        Advantages: examines range of diseases beyond those that cause death

·        Disadvantages:

o  Diagnosis can be ambiguous

o  Variation in recognition or reporting of disease

Self-reported or Self-rated Health Status

·        More subjective

·        Overlaps with health-related quality of life, encompassing physical health, psychological well-being, emotional well-being and social functioning

·        For assessing Maori health need to incorporate relations with extended family and spirituality (obviously non-Maori are not spiritual and don‟t care about family!!)

Composite Measures of Health Status

·        Independent Life Expectancy: average number of years living without disability. Equals life expectancy + prevalence of dependency. Ignores reversibility of some disabilities and transition from good to poor health

·        Measures of the burden of disease:

o  Takes into account fatal and non-fatal outcomes

o  Disability Adjusted Life Years:

§  Estimate of years of healthy life lost 

§  Similar to QALYs but standardised for use between populations and they also use age weights (lower weights in childhood and elderly) 

§  Used to assess the burden associated with certain diseases or with particular risk factors (eg smoking) 

§  In NZ, CV disease accounts for 24% of DALYS lost, followed by cancers and mental disorders

o  Criticisms:

§  Limited use to policy makers because they focus on health loss rather than potential gains

§  Don‟t take into account disability associated simply with old age

§  Requires extensive epidemiological data