Module 2 Flashcards
Epidemiology
Study of distribution and determinants of health-related states or events in specified populations and application of this study to control of health problems
Importance of pop. Health
Lifestyle, environment and public health improvements play significant roles in health + mortality
Aim of public/population health framework
Provide max. Benefit for largest no. People at same time reducing inequities in distribution of health and wellbeing
“Define problem” study
Cross-sectional
“Identify risk and protective factors” study
Cohort and case-control
“Develop and test prevention strategies” study
RCT and diagnostic test accuracy
“Assure widespread adoption” study
Evaluative studies
Preventative action can be
Put in place before identifying causative factor
- knowledge of complete pathway is not a pre-requisite for introducing preventative measures”
- can help reduce disease occurrence in pop.
James Lind’s experiment
One of earliest controlled trial although patient no. Were very low
- example of prevention before identifying cause (vitamin C deficiency)
Causal relationships
Epidemiology examines relationships/association between exposures and outcomes for this purpose but remember correlation/association doesn’t always = causation
Determining causality
- can NOT be proven in human studies (practical and ethical reasons)
- most non-experimental in ‘noisy’ environments thus must beware of errors
Bradford Hill framework - aid to thought
1) temporality
2) strength of association
3) consistency of association
4) biological gradient/dose-response
5) biological plausibility of association
6) specificity of association
7) reversibility
Temporality
Cause THEN outcome
- easier in cohort than cross-sectional/case-control studies
Strength of association
Measured by size of relative risk
Dose-response
Incremental change in exposure = change in disease rates
- linear dose-response relationship
Specificity
Cause = single effect or single cause = effect
- weakest feature as health issues have multiple interacting causes and many outcomes share causes
Reversibility
Under controlled conditions (RCT), exposure change = outcome change
(Cause deleted = outcome deleted)
- strongest evidence but not always possible
Rothman’s causal pie components
Recognises multicausality
- sufficient cause
- component cause
- necessary cause
Sufficient cause (causal mechanism)
Whole pie
- min. Set of conditions
- often several factors
- 1 disease may have several sufficient causes
Component cause
Slice
- contributes towards disease causation
- insufficient alone
- interact to produce disease
Necessary cause
A component cause that MUST be present for specific disease to occur
- some diseases may not have one so a component cause will be a necessary cause
Prevention using causal pie
Blocking/removing any component cause = prevention of some cases of disease
(No need to identify every component cause)
- can intervene at any number of points in pie
Causal pie limitations
- fails to capture dose-response relations as a continuum (just series of discrete sufficient causes)
- assumes all causes are deterministic (occurrence completely determined by combo of causes without randomness)
Probabilistic concept of causation
- cause increases probability/chance that its effects will occur
- sufficient cause raises prob to 1
- necessary cause raises prob from 0
- each component cause contributes towards prob from 0 to 1
- considers environmental factors, group level effects
Counterfactual definition of causation
- presence/absence of cause ‘makes a difference’ in outcome or prob of outcome (doesn’t clarify what kind of difference like probabilistic)
- consistent with both deterministic and probabilistic phenomena
State of Māori health
1) systematic inequalities
- health outcomes
- exposure to determinants
- health system responsiveness
- representation in health workforce
2) ethnic inequalities
- can be reduced, eliminated, prevented
Causes of health inequalities
Ethnic inequalities in health fundamentally driven by unequal distribution of health risks and opportunities (social determinants)
Conventional health promotion
- based on western models
- universal formula
- simply adapted for Māori
- not grounded in Māori values and realities (land, access to traditional Kai, te reo)
- superficial vs. structural approach
- tended to benefit non-Māori to greater extent than maori
Te pae mahutonga
Fundamental components of health promotion from a Māori world view
Te pae mahutonga components
4 central stars - mauriora - Waiora - toiora - te oranga 2 pointers - nga manukura - te mana whakahaere
Mauriora
Access to te ao maori (maori world - cultural resources - indigenous dimension)
- working with communities to incorporate/revitalise traditional practices
Waiora
Environmental protection; native and social environ.
- innovative group/community programs aligning with cultural values
Whanaungatanga
Close connection between people
Toiora
Healthy lifestyle
Te oranga
Participation in society; social determinants of health
- addressing underlying issues
- not just in communities but action at political level
Nga manukura
Health professional and community leadership
- fostering, supporting, collaborating with existing leadership/knowledge in communities rather than telling people what they should do
Te mana whakahaere
- capacity for self governance (self-determination, identifying own priorities/needs, solution, sharing, putting in practice, breaking barriers)
- community control and enabling political environ.
Principles of maori health promotion
- by Māori for Māori (for everyone - not excluding)
- self determination and control
- valid models, framework, concepts - not just translated from western context but coming from Māori world view
- Māori people, values, collectives
- contemporary tools and methods
- allows for diverse realities
- focus on determinant of health - not just surface level
- evidence-based
Importance of preventing disease
Need for prevention growing as the limitations in curing disease become apparent and as the costs of medical care escalate
How epidemiology prevents disease
- unravelling causal pathway
- directing preventative action
- evaluation of effectiveness
Population based (mass) strategy
- focuses on WHOLE POP.
- control determinants of incidence in pop. As a whole
- useful for common disease or widespread cause
- characteristics of pop.
- shifts whole risk distribution
Population based (mass) strategy advantages
- radical: addresses underlying causes
- large potential benefit for whole pop.
- behaviourally appropriate
Population based (mass) strategy disadvantages
- small benefit to indiv.
- poor motivation of indiv.
- whole pop. Exposed to downside of strategy
High risk (individual) strategy
- focuses on individuals perceived to be at high risk
- indiv. Protection
- intervention well matched to indiv. And concerns
- shift distribution of high risk to more favourable direction (truncation of risk distribution)
High risk (individual) strategy advantages
- appropriate to indiv.
- indiv. Motivation
- cost effective use of resource: concentrate limited medical services and resources where needed most
High risk (individual) strategy disadvantages
- cost of screening: need to identify individuals, may be unable to identify borderlines
- palliative and temporary effect - not radical: not seek to alter underlying causes
- limited potential: weak power to predict future disease
- behaviourally inappropriate: constrained by social norms
Need for population based AND high risk strategies
- many diseases need both approaches
- competition usually unnecessary
Priority of concern should always be the discover and control of causes of incidence though
Health promotion
- address risk factors and determinants of well-being
- cover wide range of social and environmental interventions designed to benefit/protect indiv’s health and QOL
- health/wellbeing focus
- enables/empowers people to increase control over and improve health
- involves whole pop. In every day context
Alma ata 1978
Declaration for primary health care
- protect and promote health of all
- advocated health promotion approach to primary care
Prerequisites for health
Peace and safety from violence, shelter, education, food, income and economic support, stable ecosystem and sustainable resources, social justice and equity
- all don’t have to be met before health promotion program but success depends on fulfilment
Ottawa charter for health promotion
‘Mobilise action for community development’
Acknowledges health is
- fundamental right for everybody
- requires both individual and collective responsibility
- opportunity to have good health should be equally available
- good health is an essential element of social and economic development
Building healthy public policy
- Protect health, individuals, communities to enable them to make easier choices regarding health
- Giving opportunity to make easier healthy choices
- Often done through regulations and legislations
- Making health as an important aspect of all policies (not limited to health sector/health laws)
Reorient health services
- Focussed more on support on need of people for healthy life
- Strengthening protective factors and reducing other risk factors
- Diversify
Creating supportive environ.
Natural, physical, social setting - WHERE you are, live, work etc.
Develop personal skills
- individual empowerment
- training
Strengthen community action
Community empowerment
Ottawa charter 3 basic strategies
Enable, advocate, mediate
Enable
- To provide equal opportunities/resources for all individuals to make healthy choices through access to information, life skills and supportive environments
- individual level strategy
- Cannot achieve fullest health potential unless able to take control of things that determine health
Advocate
- To create favourable political, economic, social, cultural and physical environments by promoting/ advocating for health and focusing on achieving equity in health
- system level strategy
Mediate
- To facilitate/bring together individuals, groups and parties (governments, health and other social/economic sectors, nongovernmental and voluntary organisations, local authorities, industries, media) with opposing interests to work together/ come to a compromise for the promotion of health
- strategy that joins individuals, groups and systems
Disease prevention
- disease focus
- looks at particular disease/injuries + ways of preventing them
Natural history of disease and prevention strategies
Primary: between exposure and biological onset
- control specific causes and risk factors
- vacc
Secondary: between biological onset and clinical diagnosis
- reduce more serious consequences
- screening
Tertiary: between clinical diagnosis and outcome
- reduce progress of complications
- rehab
Health protection
- Predominantly environmental hazard focused
- Risk/Hazard assessment
- Occupational health & Monitoring
- Risk communication
Screening
Involves identifying risk factors for disease, unrecognised disease or complication of disease by applying tests in a large scale to a pop.
- can be prim. Sec. Tert. As prevention strategy depending on what is screened for
Objective screening initiative
Improve health outcome (morbidity, mortality and/or disability)
Screening criteria
Suitable disease, test, treatment, screening programme
Suitable disease
A. Important public health problem
- relatively common
- relatively uncommon esp. if known that early detection/intervention = better outcome
B. Knowledge of natural history of disease/relationship between risk factors and condition
- detectable early
- increase duration of pre-clinical phase
Suitable test
Reliable, safe, simple, affordable, acceptable, accurate
Test accuracy measured through
Diagnostic test accuracy studies - tests screening against gold standard
Sensitivity
- Likelihood of +ve test in those with disease
- Test’s ability to correctly identify disease from all with disease
= true positives/all with disease = a/(a+c)
Specificity
- likelihood of -ve test in those without disease
- test’s ability to correctly identify no disease from all free from disease
= true negatives/all without disease = d/b+d
Sensitivity and specificity are
Fixed characteristics of test
Positive predictive value (PPV)
Probability of disease if positive test
= true positives/all who test positive = a/a+b
Negative predictive value (NPV)
Probability of no disease if negative test
= true negatives/all who test negative = d/c+d
PPV and NPV are
Not fixed characteristics of test
- reflects both accuracy AND disease prevalence
Prevalence and false values
- high prevalence = higher false negative
- low prevalence = higher false positive
Suitable treatment
- Evidence of early treatment = better outcomes
- Effective, acceptable and accessible treatment
- Evidence-based policies covering who should be offered treatment and what appropriate treatment to be offered
Suitable screening programme
- Benefits must outweigh harm
- RCT evidence that screening programme will result in:
reduced mortality
increased survival time - Adequate resourcing and agreed policy for testing, diagnosis, treatment and programme management
- Cost effective
- Health care system must be able to support all elements of the screening pathway
- Needs to reach all those who are likely to benefit from it (might require specific initiatives for particular population groups)
Biases when using increased survival time as measure of success of screening programmes
Lead time bias: early detection by screening may give false impression of increased life expectancy
Length time bias: calculating mean survival from screened patients (more likely to identify slow progressing diseases) gives impression of longer average survival
Requirement for prioritisation
Limited resources/funds so must distribute/spend wisely
- is distribution such that all groups have equal opportunity in achieving best health outcomes?
Distribution of healthcare funds in NZ
1) Services of curative and rehabilitative care
2) Services of long-term nursing care
3) Medical goods dispensed to outpatients
4) Prevention and public health services
5) Ancillary services to health care
6) Health administration and health insurance
Info used to establish PopHlth priorities
1) evidence-based measures
2) community expectations
3) public attitudes
4) human rights and social justice
Types of evidence-based measures
- descriptive evidence
- explanatory evidence
- evaluative evidence
descriptive evidence
Define problem - who is most/least affected? - where are we now? - where have we come from? - where are we going? Death rates/trends used
Explanatory evidence
- What are the determinants? Risks?
- Why are we getting worse/better?
- Why are pop.s different?
Equity - Does the problem/risk factor disproportionately affect pop sub groups? Why?
- Treaty of waitangi - maori
Epidemiological measures used in prioritisation
- age at death/premature mortality
- time lived with disability
- population attributable risk (PAR)
Age at death
Years of potential life lost to death (YLL)
Time lived with disability
Years lived with a disability (YLD)
Attributable risk (AR)
Risk difference
- Amount of “extra” disease attributable to a particular risk factor in the exposed group
- Used if wanting to prioritise interventions to those who are exposed to risk factor (high risk group)
Population attributable risk (PAR)
- Amount of “extra” disease attributable to a particular risk factor in a particular population
- if association causal: Amount of disease (theoretically) we could prevent if we removed the particular risk factor from the pop
- Used if wanting to prioritise intervention to whole pop
PAR equation
PAR = PGO - CGO
= a+b/P - b/CG
PAR and prevalence
Directly related
- increasing prevalence = increasing PAR
Evaluative evidence
- What can improve health outcomes and in whom?
- Is the intervention improving health outcomes?
- how well can problem be solved?
(target population, expected number in population who will be reached, evidence of effectiveness (based on known success rates), cost)
Evaluative evidence: economic feasibility
- make economic sense to address problem?
- economic consequences if not carried out?
Community expectations and values
What do communities want?
- Confidence in health system
- Access to necessary care
- Fair treatment
- Culturally appropriate
- Good info about options
- people able to make their own choices
Public attitudes
Acceptability
- Will the community and/or target pop accept the problem being addressed?
- Competing interests
- do the people have other more important matters
Human rights and social justice
Treaty of Waitangi
Caution with evidence-based considerations
Often too focussed
- while valuable, need to be mindful of communities to achieve desired outcomes despite best evidence
