Lecture 12 - Establishing causality in population health Flashcards
Why is establishing causal relationships important
Provide support for evidence-based practice
What did James Lind’s experiment teach us
The experiment showed us how sometimes preventive action can be taken before the cause of a disease is identified
Why can’t causality be proved in human experimental studies
For practical and ethical reasons
3
Most epidemiological studies…
- non-experimental
- conducted in ‘noisy’ environments in free-living populations
- determine relationship/association between a given exposure to a cause/s and dis-ease outcomes in populations
Epidemiological studies can identify a _____ _______ between a potential ____ and an _____.
Statistical association, exposure, outcome
What do we need when looking for links between exposure and outcome
- Need sufficient studies done in diverse settings and adequately limiting random errors, non-random erros, and confounding
What are the seven aspects of the Bradford Hill Framework (1965)
- Temporality
- Strength of association
- Reversibility
- Biological gradient
- Biological plausability of association
- consistency of association
- specifity of association
What is temporality
- First the cause, the the disease
- essential to establish a causal relationship
What is strength of association
The stronger the association, the more likely to be casual in absence of known biases (selection, information, and confounding)
What is reversibility
The demonstration that under controlled conditions, changing the exposure causes a change in the outcome
What is biological gradient
- incremental change in disease rates in conjunction with corresponding changes in exposure
What is biological plausability of association
- does the association make sense biologically
- e.g the chemicals in tobacco are know to promote cancers
What is consistency of association
Replication of the findings by different investigators, at different times, in different places, with different methods.
(multiple studies show similar results)
What is specifity of association
- a cause leads to a single effect
- an effect has a single cause
Why is specifity of association the weakest criteria
Many diseases share causes, and diseases have multiple causes. What the criteria states is never the case.
What are the three elements that are a part of the epidemiological triad
Host (persons in a population), environment (physical, social, policy) and agent (biological, nutritional, physical, chemical)
What is a cause of a disease (Rothman’s causal pie model)
An event, condition, characteristic (or combination of these factors) which play an essential role in producing the disease.
What does the causal pie recognise
Multi-causality
What is a sufficient cause
- The whole pie
- A minimum set of conditions without any one of which the disease would not occur
- A disease may have several sufficient causes
What is a component cause
- Each factor or slice
- A factor that contributes towards dis-ease causation, but is not sufficient to cause dis-ease on its own
- Component causes ‘interact’ to produce disease
What is a necessary cause and how is it linked to component cause
- A factor (or component cause) that must be present for a specific disease to occur
- A component cause will be a necessary cause for some diseases
What would blocking/removing any component cause do
Result in prevention of some cases of disease
Do we need to identify every component cause to prevent some cases of disease
No
Is it possible to intervene at any number of points in the pie
Yes
Is the knowledge of the complete pathway a pre-requisite for introducing preventitive measures
No
What are the weaknesses of the causal pie model
- fails to capture the dose-response relations as a continuum
- assumes that all causes are deterministic (A causes B, B happens when A occurs)
What is the probabilistic concept of causation
- A cause increases the probability (or chance) that its effect will occur
- does not exclude necessary and sufficient causes
A sufficient cause raises the probability to what
1
Probability of an effect/outcome happening
- A sufficient cause raises probability to 1
- A necessary cause raiss that probability from 0
- each component cause contibutes towards the probability from 0 to 1
A necessary cause raises that probabilty of
What are the causes of the causes (for individuals)
Any event, characteristic or other definable entity, that brings about a change for better or worse in health
What are the possible events for the causes of the causes for individuals
- income
- employment
- education
- housing and neighbourhoods
- societal characteristics e.g racism
- autonomy and empowerement - social cohesion
may vary at different life-stages
How it differs (and similars) to individuals causes of the causes
What are the causes of the causes (for populations)
Concepts are similar for individuals, but nature of determinants is often different
* not just application of the individual perspective to whole population, but includes characteristics of the population itself
* also related to the context of the population
What are downstream determinants
- A determinant of health that is proximate or near to the change in health status
- ‘near’ generally refers to any determinant that is readily and directly associated with an immediate cause of disease
What are downstream determinants often referred to (and provide examples)
Proximal causes e.g lifestyle and behavioural factors related to nutritiion, like smoking
What are upstream determinants
- a determinant of health that is either distant in time and/or place from the change in health status
What are upstream determinants often referred to as (and prove an example)
Distal causes e.g national, political, legal and cultural factors that indirectly infleunce health by acting on downstream determinants
Would upstream or downstream determinants be something that you can change today
Downstream
How do downstream interventions operate
Operate at the micro (proximal) level, including treatment systems, and disease management (address downstream determinants)
How do upstream interventions operate
At macro (distal) level, such as government policies and international trade agreements (address upstream determinants)
How do upstream interventions impact our lives
They are things we cant change overnight, but impact our behaviours e.g government policies
Describe level 1 of the D&W model - the individual
- Age, sex, constitutional factors and individual lifestyle factors
- sometimes referred to as non-modifiable determinants (gene and biology)
There are important distinctions between the impact on individuals and populations
- single gene disorders = rare among the population
- polygenic inheritance = influences likelihood of offspring developing a disease
What is habitus in level 1 of the D&W model
Lifestyle, values, dispositions and expectation of particular social groups ‘learned’ through everyday activities
* Abillity to change behaviours cary by social group
What is level 2 of the D&W model
Social and community networks and living and working conditions
How do family and friens affect our behaviours
- in developing ‘normative’ behaviours
- attitudes and behaviours of people in working community influences sense of what is normal and acceptable
What is social capital
The value of social networks that facilitates bonds between similar groups of people.
What does social capital provide
Inclusive environment for people from diverse backgrounds
What is Level 3 of the D&W model
Physical, built, cultural, biological, political environment and the ecosystem.
What is natural capital
Refers to all aspects of the natural environment needed to support life and human activity.
Refers to land, soil, water, plants and animals, as well as minerals and energy resources
What is social capital
The norms and values that underpin society.
Includes things like trust, the rule of law, the Crown-Māori relationship, cultural identity and the connections between the people and communities.
What is human capital
People’s skills, knowledge and physical and mental health.
Things that enable people to participate fully in work, study, recreation and in society more broadly.
What is financial capital
Includes things like houses, roads, buildings, hospitals, factories, equipment, and vehicles.
Make up the countries physical and financial assets which have a direct role in supporting incomes and material living conditions.
What is ‘structure’ in population and health
- Social and physical environment conditions/patterns (i.e social determinants) that influence choices and opportunities available
What is ‘agency’ in population health
The capacity of an individual/community to act independently and make free choices.
What is structure and agency needed for
Distinguish between different determinants in framework. For D&W model, structure is upstream and agency is choices.
What is the D&W framework used for
Help idenitify determinants of health (risk of protective factors of disease) and consider levels of intervention.
What does the D&W model recognise
Determinants operate at different scales
* Upstream (distal) or downstream (proximal)
* Micro (individual), meso (family, living, work), macro (national/global)
Measure trends in
Why do we need population data
- births
- mortality
- morbidity
- migration
more appplied work
Why do we need population data
- uneployment/benefit claimants
- crime
- health service utilisatin
- voter turnout
- education pathways
What is socio-economic position
The social and economic factors that influence what positions individuals or groups hold within the structure of society
What three things must determinants in SEP be
Objective, measurable and meaningful
Why measure SEP
- quantify level of inequality within or between societies
- highlight changes to population structures over time
- understand relationship between health and other social variables
- associated with health and life chances for as long as social groups have existed
What are the main causes of the causes to measure SEP for individuals
- education
- income
- occupation
- housing
- assets and wealth
- area measures (deprivation, access)
- population measures (income inequality, literacy rates, GDP)
What is deprivation
State of observable and demonstratable disadvantage relative to the local community of wider society or nation to which an individual, family or group belongs
Another way of
Area-level deprivation
Another way of measuring people’s relative position in society
Deprivation should be applied to what
Conditionss and quality of life that are of lower standard that is ordinary in a particular society
What does living in poverty refer to
Lack of income and resources to obtain the normative standard of living
What is the advantage of prioritised output
Ensures that where some need exists to assign people to a single ethnic group, ethnic groups of policy importance or of small size, are not swmaped by the NZ european ethnic group.
Produces data that is easy to work with as each individual appears only once. This means that sum of the ethnic group will add to the total NZ population
What are the disadvantages/limitations of prioritised output
It places people in specific ethnic group, which simplifies yet biasses the resulting statistics as it over-represents some groups at the expense of others.
It is an externally applied single ethnicity which is inconsistent with the concept of self-identification.
What are the advantages of total response output
Has potential to repreent people who do not identify with any given ethnic group, depending on the level of detal reported
What are the advantages/limitations to total response output
Creates complexities in the distribution of finding based on population numbers or in monitoring changes in the ethnic composition of a population in health.
Create issues in interpretation of data reported by ethnic groupings, where comparisonsbetween groups include overlapping data.
What is numerical ageing
The absolute increase in the population that is elderly.
* reflects previous demographic patterns
* improvements in life expectancy
What is structural ageing
The increase in the proportion of the population that is elderly.
How does a natural decline of the population occur
Occurs when there are more deaths than births in a population.
This is due to a combination of absolute and structural ageing (more elderly = more deaths)
How does an absolute decline of the population occur
Occurs when there is insufficient migration to replace the ‘lost’ births and increased deaths
