PUBLIC HEALTH Flashcards
PREVENTION + SCREENING
What is primary prevention?
Give some examples.
Preventing a disease from occurring in the first place.
E.g. change4life, 5-a-day, vaccines > they eliminate risk factors contributing.
PREVENTION + SCREENING
What is secondary prevention?
Give some examples
Detecting a disease in its early or pre-clinical phase to alter its course + improve health outcomes.
E.g. all screening programmes (breast, bowel, cervical cancer, heel prick in infants).
PREVENTION + SCREENING
What is tertiary prevention?
Give some examples
Attempting to slow down disease progression + prevent complications of a disease, helping people manage their illness effectively.
E.g. diabetic foot care, attending rehab after a stroke to prevent immobility.
PREVENTION + SCREENING
What are the 2 approaches to prevention?
- Population approach.
- High risk approach.
PREVENTION + SCREENING
Explain the population approach to prevention.
Give some examples.
Preventative measure delivered on a population wide basis + seeks to shift the risk factor distribution curve.
E.g. dietary salt reduction via legislation to reduce BP, adding iodine to salt to prevent iodine deficiency
PREVENTION + SCREENING
Explain the high risk approach to prevention.
Give some examples
Identifying individuals above a chosen cut-off + treating them.
E.g. screening for HTN + treating them.
PREVENTION + SCREENING
What is meant by the prevention paradox?
A preventative measure which brings much benefit to the population often offers little to each participating individual.
I.e. it’s about screening a large number of ppl to help a small number of ppl.
PREVENTION + SCREENING
What is the concept of screening?
A process which identifies seemingly well individuals who may be at risk of a disease, in the hope of catching the disease at its early stage.
- It’s not a diagnostic process, simply a means of assessing risk + catching diseases in their early stage.
PREVENTION + SCREENING
In the grid of Disease vs. screening test – what does a, b, c + d stand for?
A = true positive. B = false positive. C = false negative. D = true negative.
PREVENTION + SCREENING
Define sensitivity.
The proportion of people with the disease who are correctly identified by the screening test. a ÷ (a + c)
PREVENTION + SCREENING
Define specificity.
The proportion of people without the disease who are correctly excluded by the screening test. d ÷ (d + b)
PREVENTION + SCREENING
Define positive predictive value (PPV).
The proportion with a positive test result who actually have the disease. Dependent on underlying prevalence.
a ÷ (a + b)
PREVENTION + SCREENING
Define negative predictive value (NPV).
The proportion with a negative test result who do not have the disease. This is lower if the prevalence is higher. d ÷ (c + d)
PREVENTION + SCREENING
What are some types of screening available?
- Population-based screening programmes (e.g. cervical, breast cancer).
- Opportunistic screening (e.g. BP measurements in GP).
- Screening for communicable disease.
- Pre-employment + occupational medicals.
- Commercially provided screening (e.g. pay company to send off blood + get tested for a variety of different genetic issues).
- Genetic counselling (genetic testing for people with FHx of diseases).
PREVENTION + SCREENING
What are some of the disadvantages of screening?
- Exposure of well individuals to distressing or harmful diagnostic tests.
- Detection + treatment of sub-clinical disease that may have never caused any problems.
- Preventative interventions that may cause harm to the individual or population.
PREVENTION + SCREENING
What are the Wilson + Junger criteria for screening?
- Condition should be an important health problem.
- There should be an accepted treatment available.
- Facilities for Dx + Tx should be available.
- There should be a recognisable latent or early symptomatic stage.
- There should be a suitable test or examination.
- The test should be acceptable to the population.
- The natural Hx of the condition should be understood.
- There should be a policy on whom to treat as pts.
- The costs of screening should be economically balanced.
- Screening should be a continuous process, not just a one off.
PREVENTION + SCREENING
What 2 types of bias may be present in screening?
- Lead-time bias.
- Length-time bias.
PREVENTION + SCREENING
Explain what lead-time bias is.
When screening identifies an outcome earlier than it would otherwise have been identified + results in an apparent increase in survival time, even if screening has no effect on the outcome.
PREVENTION + SCREENING
Explain what length-time bias is.
Bias resulting from differences in the length of time taken for a condition to progress to severe effects that may affect the apparent efficacy of a screening method.
E.g. less aggressive cancers w/ longer presentations are more likely to be detected by screening. Comparing survival in screen detected + non-screen detected pts may be biased as there’s a tendency to compare less aggressive + more aggressive cancers.
STUDY DESIGN
What is the methodology behind an ecological study?
- Descriptive/observational study design comprising of case reports or case series studying population/groups rather than individuals. COMPARATIVE
- Uses routinely collected data to show trends in data – often associations between occurrence of disease + exposure to known or suspected causes.
STUDY DESIGN
What are the advantages of an ecological study?
- Few ethical issues.
- Useful for generating hypotheses.
- Uses routine data so quick + cheap.
- Can show prevalence + association.
STUDY DESIGN
What are the disadvantages of an ecological study?
- Cannot show causation.
- Bias (variation in diagnostic criteria).
- Inconsistency in data presentation.
STUDY DESIGN
What is the methodology behind a cross-sectional study?
- Prevalence study.
- Descriptive + analytical study design used to generate hypotheses.
- Divides the population into those without the disease + those with the disease + collects data on them once at a defined time to find associations at that single point in time.
STUDY DESIGN
What are the advantages of a cross-sectional study?
- Relatively cheap + quick.
- Provide data on prevalence at a single point in time.
- Good for surveillance + public health planning.
- Large sample size.
STUDY DESIGN
What are the disadvantages of a cross-sectional study?
- Risk of reverse causality.
- Cannot measure incidence as no time reference.
- Risk of recall bias + non-response.
STUDY DESIGN
What is the methodology behind a case control study?
- A type of analytical study (retrospective).
- Takes people with a disease + matches them to people without the disease for same age/sex/class etc + Studies previous exposure to the agent in question.
STUDY DESIGN
What are the advantages of a case control study?
- Quicker than cohort of intervention studies as it’s retrospective.
- Inexpensive, good for rare outcomes (e.g. cancer).
- Can investigate multiple exposures.
STUDY DESIGN
What are the disadvantages of a case control study?
- Retrospective nature only shows an association (not causation).
- Difficulty finding controls to match with cases.
- Unreliable due to recall bias.
- Prone to selection + information bias.
STUDY DESIGN
What is the methodology behind a cohort study?
- Incidence study (prospective).
- Start with a population without the disease in question + study them over time to see if they are exposed to the agent in question + if they develop the disease in question or not.
STUDY DESIGN
What are the advantages of a cohort study?
- Prospective so can show causation.
- Lower chance of selection + recall bias.
- Absolute, relative + attributable risks can be determined.
- Good for common + multiple outcomes.
STUDY DESIGN
What are the disadvantages of a cohort study?
- Loss to follow-up, requires a control group to establish causation.
- Takes a long time, need a large sample size.
STUDY DESIGN
What is the methodology behind a randomised control trial?
- Pts are randomised into groups.
- One group is given an intervention (interventional group).
- One group is given a placebo/control (control group).
- Then, the outcome is measured. Often blind or double blind.
STUDY DESIGN
What are the advantages of a randomised control trial?
- Can infer causality (gold standard).
- Randomisation allows confounding factors to be equally distributed + biases minimised (helped by blinding).
STUDY DESIGN
What are the disadvantages of a randomised control trial?
- Is it ethical to withhold a treatment that is strongly believed to be effective?
- Time consuming, expensive.
- Volunteer bias – specific inclusion/exclusion criteria may mean the study population is different from typical pts (e.g. excluding very elderly pts).
STUDY DESIGN
What is the methodology behind a meta-analysis? How does this differ to a systematic review?
- A statistical technique where you pool all the results of the available evidence + look at effect.
- Systematic review doesn’t involve the statistical procedure.
EPIDEMIOLOGY
Define epidemiology. What factors are considered when measuring epidemiology of a disease?
The study of the frequency, distribution + determinants of disease + health-related states in populations in order to prevent + control disease.
- Time, place, person (age, gender, class, ethnicity).
EPIDEMIOLOGY
Define incidence.
The number of new cases of a disease that develop in a population (e.g. per 100,000) in a given time frame (e.g. per year).
EPIDEMIOLOGY
Define prevalence.
The total # of people in a population found to have a disease at a point in time.
- Number of existing cases/population/points in time.
EPIDEMIOLOGY
What is meant by person-time?
The measure of time at risk i.e. time from entry to a study to:
- Disease onset.
- Loss to follow up.
- End of study.
It is the sum of each individual’s time at risk (i.e. length of time they were followed up in the study).
EPIDEMIOLOGY
How do you calculate incidence rate calculations?
# of persons who have become cases in a given time period ÷ total person-time at risk during that period. - Person-time is the denominator in them.
EPIDEMIOLOGY
What is the denominator in cumulative incidence calculations?
Number of disease-free at start of study.
EPIDEMIOLOGY
What is meant by:
i) an independent variable?
ii) a dependent variable?
i) A variable that can be altered in a study.
ii) A variable that is dependent on the independent variables or one that cannot be altered.
EPIDEMIOLOGY
What is meant by absolute risk?
Gives a feel for actual numbers involved i.e. it has units.
- E.g. deaths/1000 population.
EPIDEMIOLOGY
What is meant by relative risk?
Ratio of risk of disease in the exposed to the risk in the unexposed i.e. no units.
- It tells us about the strength of association between a risk factor + a disease.
EPIDEMIOLOGY
How do you calculate relative risk?
Incidence in exposed ÷ incidence in unexposed.
EPIDEMIOLOGY
What is meant by attributable risk?
The rate of disease in the exposed that may be attributed to the exposure.
- Attributable risk is a type of absolute risk (absolute excess risk).
- It’s about the size of effect in absolute terms i.e. gives a feel for the public health impact (if causality assumed).
EPIDEMIOLOGY
How do you calculate attributable risk?
Incidence in exposed – incidence in unexposed.
EPIDEMIOLOGY
What is meant by relative risk reduction?
The reduction in rate of the outcome in the intervention group relative to the control group.
EPIDEMIOLOGY
How do you calculate relative risk reduction?
(Incidence in unexposed – incidence in exposed) ÷ incidence in unexposed.
- (ARR ÷ incidence in unexposed).
EPIDEMIOLOGY
What is meant by absolute risk reduction?
The absolute difference in the rates of events between the 2 groups. Gives an indication of the baseline risk + the intervention effect.
EPIDEMIOLOGY
Give an example of absolute risk reduction?
Assuming exposed means they have had a particular intervention (such as giving statins to people with hypercholesterolaemia) + then a control group who do not have statins + seeing how many in each group have a heart attack to see if the intervention of statins is effective.
EPIDEMIOLOGY
How do you calculate absolute risk reduction?
Incidence in unexposed – incidence in exposed.
EPIDEMIOLOGY
What is meant by odds?
The odds of an event is the ratio of the probability of an occurrence compared to the probability of a non-occurrence.
EPIDEMIOLOGY
How do you calculate odds?
Probability ÷ (1 – probability).
EPIDEMIOLOGY
What is meant by odds ratio?
The ratio of odds for the exposed group to the odds for the non-exposed groups.
- Or can be interpreted as a relative risk when the event is rare.
EPIDEMIOLOGY
When would odds ratio be used?
For case control studies as it’s not possible to calculate the relative risk.
- For cross-sectional + cohort studies – both can be derived but odds ratio is used if it’s not clear which is the independent/dependent variable.
EPIDEMIOLOGY
How do you calculate odds ratio?
(P exposed ÷ [1 – P exposed]) ÷ (P unexposed ÷ [1 – P unexposed])
EPIDEMIOLOGY
What is meant by number needed to treat?
The number of patients that need to be treated in order to prevent one bad outcome.
EPIDEMIOLOGY
How do you calculate NNT?
1 ÷ ARR (risk in unexposed – risk in exposed)
EPIDEMIOLOGY
Define bias.
A systematic deviation from the true estimation of the association between exposure + outcome.
I.e. systematic error > distortion of the true underlying association.
EPIDEMIOLOGY
What are the 2 main types of bias?
- Selection bias.
- Information (measurement) bias.
EPIDEMIOLOGY
What is selection bias?
Give some examples.
- A systematic error either in the selection of study participants or the allocation of participants to different study groups.
- Non-response, loss to follow up.
- Those in the intervention group different in some way from the controls other than the exposure in question.
EPIDEMIOLOGY
What is information bias?
Give some examples of sources of information bias.
A systematic error in the measurement or classification of exposure or outcome.
- Observer (observer bias).
- Past event incorrectly remembered (recall bias).
- Responder does not tell the truth (reporting bias).
- Wrongly calibrated instrument (measurement bias).
EPIDEMIOLOGY
What type of bias can occur after a study is completed?
Publication bias where some trials are more likely to be published than others.
EPIDEMIOLOGY
What is confounding?
What is the effect of confounding on a study?
Where a factor is associated with the exposure of interest + independently influences the outcome but does not lie on the causal pathway.
- May affect the validity of a study.
EPIDEMIOLOGY
What is the Bradford-Hill criteria for assessing causality?
- Strength of association (the magnitude of the RR).
- Dose response (the higher the exposure, the higher the risk of disease).
- Consistency (similar results from different researches using various study designs).
- Temporality (does exposure precede outcome?)
- Reversibility (experiment) – removal of exposure reduces risk of disease).
- Biological plausibility (biological mechanisms explaining the link).
- Coherence (logical consistency with other information).
- Analogy (similarly with other established cause-effect relationships).
- Specificity (relationship specific to outcome of interest).
EPIDEMIOLOGY
If association is not causal, how could it be explained?
- Bias.
- Chance.
- Confounding.
- Reverse causality.
- A true causal association.
EPIDEMIOLOGY
What is meant by reverse causality?
Give an example.
Refers to a situation when an association between an exposure + outcome could be due to the outcome causing exposure rather than the other way.
- E.g. case study showing stress causes HTN but HTN could cause increased stress.
HEALTH DETERMINANTS ETC.
Define epigenetics.
The study of how genes interact with the environment.
- Changes in organisms caused by modification of gene expression rather than alteration of the genetic code itself.
HEALTH DETERMINANTS ETC.
Define allostasis.
The stability through change, or homeostasis, of our physiological systems to adapt rapidly to change in environment.
HEALTH DETERMINANTS ETC.
Define allostatic load.
Long-term over-taxation of our physiological systems leading to impaired health (stress).
- The price we pay for allostasis.
HEALTH DETERMINANTS ETC.
Define public health.
Defined as the science + art of preventing disease, prolonging life + promoting health through organised efforts of society.
- Population perspective – thinks in terms of groups, not individuals.
HEALTH DETERMINANTS ETC.
What are the key concerns of public health?
- Inequalities in health.
- Wider determinants of health.
- Prevention.
HEALTH DETERMINANTS ETC.
What are the determinants of health?
- Genes (age, gender, ethnicity).
- Environment (physical + social + economic > housing, education).
- Lifestyle (smoking, wealth, employment).
- Access to healthcare (economic factors, access, quality).
HEALTH DETERMINANTS ETC.
What are the wider/social determinants of health?
- Education, socioeconomic status, unemployment, housing, physical environment etc.
HEALTH DETERMINANTS ETC.
What are the 3 domains of public health?
- Health improvement.
- Health protection.
- Improving services.
HEALTH DETERMINANTS ETC.
What is meant by health improvement.
What does it encompass?
Societal interventions aimed at preventing disease, promoting health + reducing inequality.
- Inequalities, education, housing, employment, lifestyles, family/community, surveillance + monitoring of some diseases + risk factors (imms, smoking, screening)
HEALTH DETERMINANTS ETC.
What is meant by health protection.
What does it encompass?
Measures to control infectious disease risks + environmental hazards.
- Infectious diseases, chemicals + poisons, radiation, emergency response, environmental health hazards.
HEALTH DETERMINANTS ETC.
What is meant by improving services.
What does it encompass?
Organisation + delivery of safe, high quality services for prevention, treatment + care.
- Clinical effectiveness, efficiency, service planning, audit + evaluation, clinical governance, equity.
HEALTH DETERMINANTS ETC.
What are the 5 levels of Maslow’s hierarchy of needs?
- Physiological = breathing, food, water, sleep.
- Safety = security of employment, resources, family health, property.
- Love/belonging = friendship, family, sexual intimacy.
- Esteem = self-esteem, confidence, achievement, respect.
- Self-actualisation = morality, creativity, spontaneity, problem solving, lack of prejudice, acceptable of facts.
HEALTH DETERMINANTS ETC.
What are health interventions?
Give some examples.
Any tactics that are done to improve public health.
- Health promotion/awareness campaigns (Change4Life, 5-a-day, Stoptober, Movember).
- Promoting screening + immunisations (cervical smear, MMR vaccine).
HEALTH DETERMINANTS ETC.
What are the 3 levels of intervention?
- Individual = pt centred approach to care.
- Community = community centred approach to care.
- Population = delivered nationwide, non-specific to individuals.
HEALTH DETERMINANTS ETC.
Give some examples of the 3 levels of intervention.
- Individual = immunisations.
- Community = new outdoor play area in a particular village, more cycle paths to make cycling safer.
- Population = iodine in salt to prevent iodine deficiency, PH campaigns (Change4Life), screening, vaccines.
HEALTH DETERMINANTS ETC.
Explain how the effects of interventions are rarely restricted to one level.
Brief GP intervention aimed at reducing alcohol consumption.
- Individual = level of alcohol consumption, incidence of domestic violence.
- Community = local alcohol sales, alcohol-related crime.
- Population = national alcohol sale, national stats on alcohol-related crime.