Module 3: Measuring Health in Populations Flashcards
Define epidemiology.
The study of the occurrence and distribution of health-related events, states or processes in specified populations.
Define population health.
The health outcomes of a group of individuals including the distribution of such outcomes within the group.
What can we see when viewing health by the population?
Patterns in the big picture.
What is a major difference between Maori and non-Maori populations in NZ?
Life expectancy differs by 7 years on the population level.
Name two important patterns of health distribution in NZ.
Ethnicity
Socioeconomic status
What is NZDep?
A measure of deprivation based on areas of about 100-200 people. The areas are classed into deciles 1 through 10, with about 10% of the population in each one.
Name some variables included in NZDep2018.
Communication (internet) Income and benefits Employment Qualifications Owned home Support (single parent family) Living space and condition
Which factors can we look at when assessing socioeconomic status?
Deprivation Occupation Income Education Living standards measures
Describe the difference between absolute and relative poverty.
Absolute poverty is at an income level below what is needed for basic necessities of life.
Relative poverty is at an income level below what is needed for basic necessities relative to the society/ economy.
What must we keep in mind when using the NZDep to make judgements?
It is a neighbourhood measure, not individual measure.
What health statistic can we see across the globe?
A social gradient- decreasing health with increasing deprivation.
Define social determinants of health.
The conditions in which people are born, grow, live, work and age, and the wider set of forces and systems shaping the conditions of daily life.
Describe the Dahlgren Whitehead 1991 model.
A model of the social determinants of health.
Centre: age, sex and hereditary factors
2nd: Individual lifestyle factors (diet, smoking, exercise)
3rd: Social and community influences (what others do)
4th: Living and working conditions (housing, type of work)
Outside: General socioeconomic, cultural and environmental conditions (e.g. at a national level)
Which group of diseases dominated before the industrial revolution?
Communicable infectious disease
Which group of diseases dominate cause of death today?
Noncommunicable disease
Describe the main difference in cause of death between low income and high income countries.
Low income countries have a higher proportion of death caused by group 1 diseases (big 3: malaria, TB and HIV/AIDS)
Apart from management of transmission and vaccines, why do noncommunicable diseases dominate over communicable infectious diseases as cause of death?
Noncommunicable diseases are associated with old age, and we have an ageing population.
Define morbidity.
Any departure from physical and psychological wellbeing.
Define DALYs.
Disability-adjusted life years, a measure of health loss.
The sum of years of life lost from early death, and years “lost” lived with disability adjusted for severity.
One DALY represents one year lived in good health.
What can DALYs measure in a population?
The gap between a population’s current health status and ideal health status.
Define ideal health status of a population.
Entire population lives to advanced age free of disease and disability.
What is happening to DALY rate and total number of DALYs in NZ?
DALY rate is decreasing as medicine improves incidence rate.
Total number of DALYs increasing due to our ageing population, increasing disability years.
Name two population change theories.
Demographic Transition
Epidemiological Transition
What does the Demographic Transition theory explain?
Changes in population death and birth rates over time.
Growth and change in populations over time.
What does the Epidemiological Transition theory explain?
Changes in population disease patterns over time (communicable and noncommunicable diseases).
Why do we have an ageing population?
People are living longer, and the birth rate has decreased.
Why will our population continue to grow even if our birth rate is relatively low?
Migration
The Epidemiological Transition shows a large drop in communicable diseases over time. What are two key factors that have contributed to this?
Sewage systems
Increased access to clean drinking water
Life expectancy is increasing faster than health expectancy. What do we need to focus on?
We need to aim for good health in older years, not an extended period of disability. Improve quality of last years, not quantity.
What is the first step of the public health model?
Defining and measuring the problem.
Name three measures of disease occurrence in a population.
Prevalence
Incidence rate
Incidence proportion
Define prevalence.
The proportion of a population who have the disease at a given time.
Why do we measure prevalence?
To see the burden of disease on a population
To allocate health resources appropriately
Define the fraction used to determine prevalence.
No. of people with a disease at a given point in time/
Total no. of people in a population at a given point in time
Name two limitations of prevalence as a measure of disease occurrence.
Difficult to assess the development of disease.
Is influenced by the duration of disease.
What is the difference between incidence proportion and incidence rate?
The denominator used.
Incidence proportion calculates no. of new cases of disease within a period/ no. of people at risk at start of period
Incidence rate calculates no. of new cases of disease within a period/ no. of person-years at risk of developing the disease
Define incidence proportion.
The proportion of an outcome-free population that develops the outcome of interest in a specified period.
Name two limitations of incidence proportion as a measure of disease occurrence.
Assumes a ‘closed’ population. (people leaving and dying)
Highly dependent on time period.
Define incidence rate.
The rate at which new cases of the outcome of interest occur in a population.
Name two limitations of incidence rate as a measure of disease occurrence.
Person-time might not be available to calculate.
Person-time might be hard to calculate, especially with a large sample size.
What is the purpose of age standardisation?
Removes the effects of populations having different age structures, so we can compare them accurately.
How are prevalence, incidence and duration related?
P~I x D
Changes to both incidence and duration can affect prevalence.
What does descriptive epidemiology study?
The distribution of health-related states and events.
What does analytic epidemiology study?
The determinants of health-related states and events.
Describe a cross-sectional study. What does it measure?
Measures the prevalence of exposures and/or outcomes of interest from a cross-section of the group of interest.
Give three examples of cross-sectional studies in NZ.
NZ health survey
NZ census
National youth health and wellbeing surveys
What is prevalence of disease affected by?
Incidence and duration
Describe the GATE frame.
Graphic appraisal tool for epidemiological studies.
Includes source and sample, exposed and comparison groups, outcomes and time.
Name four limitations of cross-sectional studies.
Can’t determine temporal sequence (what caused what)
Doesn’t measure incidence
Difficult for studying rare outcomes or exposures
Difficult for assessing variable or transient exposures (e.g. blood pressure- always changing)
Name three strengths of cross-sectional studies.
Can assess multiple exposures and outcomes
Ideal for measuring prevalence and its distribution
Less expensive and time-consuming than other studies
Describe an ecological study.
Compares outcomes and exposures between groups (not individuals).
Name three limitations of ecological studies.
Cannot assume any individual from a group will fit the average.
Cannot control confounding
Cannot show causation
Name two strengths of ecological studies.
Good for assessing population level factors
Easy and inexpensive because data is often routinely collected
When is association between exposure and outcome present?
If the exposure increases or decreases the occurrence of the outcome.
Describe PECOT.
Population Exposure Comparison (group) Outcome Time (length of follow up)
Define relative risk. What is it good for?
Incidence with exposure/ incidence of comparison group
How many times as likely is the exposed group to develop the outcome as the comparison group?
Aetiology (causes), strength of association
Define risk difference. What is it good for?
Incidence with exposure - incidence of comparison
How many extra cases are attributable to exposure?
Impact of exposure and removal of exposure
What are the values of relative risk and risk difference if there is no association between exposure and outcome?
RR= 1 RD= 0 cases per (no.) people
What are the values of relative risk and risk difference if the exposure is a protective factor?
RR<1
RD<0 (IE
Describe a cohort study.
Individuals are allocated to exposure and comparison groups based on the presence or absence of exposure, then followed up over time to see if they got the outcome.
What can we measure from a cohort study?
Incidence proportion and rate, relative risk and risk difference.
Name three things to consider for a cohort study.
Might need to select people based on exposure if it is rare.
Participants musn’t already have the outcome of interest.
Participants may change in their exposure status.
Name four strengths of a cohort study.
Can determine temporal sequence between exposure and outcome.
Can examine multiple outcomes from an exposure.
Can calculate incidence.
Good for studying rare exposures.
Name four limitations of a cohort study.
Loss to follow up can introduce bias.
Potential for misclassification of exposures/ outcomes.
Not good for studying rare outcomes.
Time consuming and potentially expensive.
Define a historical cohort study.
A retrospective cohort study that uses existing data that has been collected for a different purpose.
Name the strengths and limitations of a historical cohort study compared to a normal cohort study.
Less time consuming- good for outcomes that take a long time to develop.
Less expensive.
Have to question quality of data- was collected for a different purpose
Can introduce selection bias for sorting exposure and comparison groups.
Describe a case-control study.
A retrospective observational analytic study where we ascertain the outcome status, then find out the exposure.
When do we prefer to use a case-control study over a cohort study?
For outcomes that are rare or slow to develop, or transient exposures.
Why do we try to identify incident cases rather than prevalent cases in a case-control study?
Because we don’t want to introduce prevalence-incidence bias: prevalence is affected by duration
Name the strends of a case-control study.
Good for studying rare outcomes and transient exposures, as well as multiple exposures.
Can determine temporal sequencing.
Quick and inexpensive.
Name the limitations of a case-control study.
Study only one outcome.
Difficult to select appropriate control group without introducing selection bias.
Susceptible to recall bias.
Describe a randomised control trial.
An analytic interventional study that tests if an intervention affects the frequency of an outcome.
Why do we use randomisation?
To avoid confounding- the influence of a different factor
Are randomisation and random selection the same thing?
No- random allocation refers to allocating the participants selected to be in the study into two groups, random selection refers to randomly selecting participants from the population to be in the study.
How do we protect randomisation?
Concealment of allocation (allocation sequence is hidden and unpredictable)
Intention-to-treat analysis (always analyse cases as they were randomised- e.g. even if they stop taking medication)
How do we avoid bias in RCTs?
Blinding
Account for loss to follow-up
Avoid nonadherence (of participants to study)
Define clinical equipoise and give examples.
Genuine uncertainty about benefit or harm of intervention.
- harmful intervention
- intervention to test a risk factor
- treatment known to be less effective than current available treatments
What are the limitations of an RCT?
Resource intensive (time, large sample size, cost) Exposure needs to be modifiable Highly selective- hard to reflect to real world
