Public Health Flashcards
What is Public Health?
The science and art of preventing disease, prolonging life and promoting health through organised efforts of society
Define Epidemiology
The study of frequency, distribution and determinants of disease and health related states in populations in order to prevent and control disease
Define incidence
Number of new cases of a disease in a population in a given time frame (new cases per 1000 per year)
- The rate at which new disease occur in a population in a certain time period
Define Prevalence
Existing cases in a population at a point in time (total number of people with a condition per 100,000 per year)
What is Person time?
Measure of time at risk = time from entry to a study to
- Disease onset
- Loss to follow up
- End of study
Used as the denominator to calculate incidence rate
Define incidence rate
Number of person who have become cases in a given period of time / total person time at risk during that period
What is meant by absolute risk?
Actual numbers involved and has units
e.g. 50 deaths per 1000 people
What is meant by relative risk?
The ratio of risk in one category relative to another
E.g. risk in exposed compared to the risk in unexposed
Tells us the strength of association between risk factor and disease
How is relative risk calculated?
Incidence in exposed ÷ incidence in unexposed
Define attributable risk
Rate of disease in the exposure that may be attributed to the exposure
- Tells us about the size of effect in absolute terms
How is attributable risk calculated?
Incidence in exposed - incidence in unexposed
If the incidence of disease A in smokers is 1/1000 person years and 0.05/1000 person years in non smokers, what is the attributable risk?
1-0.05 = 0.95/1000 person years
If the incidence of disease A in smokers is 1/1000 person years and 0.05/1000 person years in non smokers, what is the relative risk?
1/0.05 = 20 (no units)
If the incidence of disease B is 8/1000 person years and incidence of disease B in non-smokers is 4/1000 person years what is the attributable risk?
8 - 4 = 4/1000 person years
If the incidence of disease B is 8/1000 person years and incidence of disease B in non-smokers is 4/1000 person years what is the relative risk?
8/4 = 2 (No units)
What is relative risk reduction?
Reduction in the rate of the outcome in the intervention group relative to the control group
How is relative risk reduction calculate?
1 - relative risk
OR
(incidence in non exposed - incidence in exposed) ÷ incidence in non exposed
What is absolute risk reduction?
Absolute difference in the rate of events between the 2 groups
Gives an indication fo the baseline risk and the intervention effect
How is absolute risk reduction calculate?
Incidence in non exposed - incidence in exposed
Define Number Need to Treat (NNT)
Number of patients needed to treat to prevent one bad outcome
How is NNT calculated?
1 / Absolute risk reduction
OR
1 / (incidence in non exposed - incidence in exposed)
What is meant by odds?
Odds of an event is the ratio of the probability of an occurrence compared to the probability of non-occurrence
How Is Odds calculated?
Probability / (1 - Probability)
What are the 5 factors that could be responsible if a study finds an association between exposure and an outcome?
- Bias
- Chance
- Confounding factors
- Reverse causality
- A true causal association
Define bias
A systematic deviation from the true estimation of the association between exposure and outcome
What are the 3 main types of bias?
- Selection bias
- Information (measurement) bias
- Publication bias
What is selection bias?
A systematic error in
1. Selection of study participants
2. Allocation of participants to different study groups
(those who take part may be different to those who don’t)
What are some examples of selection bias?
- Non response
- Loss to follow up
- Those in intervention group different in some ways form the controls other than the exposure in question
What is information bias?
A systematic error in the measurement or classification of the exposure or outcome
What are some potential sources of information bias?
- Observer bias
- Participant –> recall/reporting bias
- Instrument –> wrongly calibrated
Define confounding
The situation where a factor is associated with the exposure of interest and independently influences the outcome (but does NOT lie on the causal pathway)
Define reverse causality
Refers to the situation when an association between an exposure and an outcome could be due to the outcome causing the exposure rather than the exposure causing the outcome
What is the Bradford Hill criteria for causality?
- Strength of association –> magnitude of relative risk
- Dose response –> higher the exposure the higher the risk of disease
- Consistency –> similar results from different researchers using various study designs
- Temporality –> Does the exposure precede the outcome
- Reversibility –> Removal of the exposure reduces the risk of disease
- Biological plausibility –> biological mechanisms explain the link
Name 3 types of study design
- Ecological
- Cross-sectional
- Case-control
- Cohort
- Randomised control trial (RCT)
What does a descriptive study involve?
- Case reports of case series - study individuals
2. Ecological studies - use routinely collected data to show trends in data and thus useful for generating hypotheses
Which type of study uses routinely collected population level data to show trends and to generate hypotheses?
Ecological study
What is the issue with ecological studies?
Shows prevalence and association but cannot show causation
What is a cross sectional study?
Divide the population into those without the disease and those with the disease and collects dat on them at defined times to find associations at that point in time
- Used to generate hypotheses but prone to bias and have no time reference
What are the advantages of a cross sectional study?
- Quick and cheap
- Provide data on prevalence at a single point in time
- Large sample sizes
- Good for surveillance and public health planning
What are the disadvantages of cross sectional studies?
- Risk of reverse causality (don’t know whether outcome or exposure came first)
- Cannot measure incidence
- Risk of recall bias and non response
What is a case control study?
A type of retrospective analytical study that takes people with a disease and compares them to people without the disease for age/sex/habit/class etc
E.g. Researchers set out to examine the association between alcohol consumption and stroke - they identify all new patients admitted with stroke and compare their alcohol consumption with patients admitted for elective surgery
Give 2 advantages of a case control study
- Good for rare outcomes
- Quicker than cohort or intervention studies (as outcome has already happened)
- Can investigate multiple exposures
Give 2 disadvantages of a case control study
- Difficulties finding control to match with cases
2. Prone to selection and information bias
What is a cohort study?
Prospective study that starts with a population without a disease in question and study them over time to see if they are exposed to the agent in questions and if they develop the disease in question or not
Give 2 advantages of a cohort study
- Possible to distinguish preceding causes from concurrent associated factors
- Lower chance of secretion and recall bias
- Prospective - so can show causation (where retrospective can’t)
- Good for common and multiple outcomes
- Absolute, relative and attributable risk can be determined
Give 2 disadvantages of a cohort study
- Takes a long time
- Loss to follow up
- Needs a large sample size
- Requires a control group to establish causation
What is a randomised control trial?
A population are randomised into either an interventional or a control group
- Often blind or double blind trials
Give 2 advantages of a RCT
- Low risk of bias and confounding
2. Can infer causality (gold standard)
Give 2 disadvantages of a RCT
- Time consuming
- Expensive
- Specific inclusion.exclusion criteria may mean the study population is different form typical patients
- Ethical issues - is it ethical to withhold treatment that is strongly believed to be effective?
What are the main issues with controlled trials that are not randomised?
- Very subject to bias
- Confounding factors are not equally spread across the groups
Which type of study is also known as an incidence study?
A cohort study –> follows a population over time to see if they’re exposed to the agent in question and if they develop the disease
Which type of study is also known as a prevalence study?
A cross-sectional study –> looks at the population at point in time
Define Screening
A process which sort out apparently well people who are at risk of disease in hope of caching it in its early stages
- NOT diagnostic
What are the Wilson and Junger criteria for screening?
- Condition must be an important health problem
- Must have a known detectable latent phase
- Must have a known natural course/progression
- Must be a test which is acceptable to the population
- Must be a treatment for the condition
- Must be an agreed at risk population of which to screen
- Must be an agreed policy on who to treat
- Costs of screening should be economically balanced
- Facilities for diagnosis and treatment need to be available
- Screening should be a continuous process, not just a one off
What are the different types of screening?
- Population based screening programmes –> cervical cancer, breast cancer
- Opportunistic screening –> BP measurements at GP
- Screening for communicable diseases
- Preemployment and occupational medicals
- Commercially provided screening –> pay to get blood sent off and tested for genetic problems
- Genetic counselling –> genetic testing for people with FHx of genetic diseases
What are some disadvantages of screening?
- Exposure of well individuals to distressing or harmful diagnostic tests
- Detection and treatment of subclinical disease that would never have caused any problems
- Preventative interventions that may cause harm to the individuals or population
What is sensitivity and how do you calculate it?
Proportion of people with the disease are correctly identified
True positive / (True positive + False negative)
What is the specificity of screening and how do you calculate it?
Proportion of people without the disease that are correctly excluded by the screening test
True negative / (True negative + False positive)
Define Positive Predictive Value (PPV) and how is it calculated?
Proportion of people with a positive test result who actually have the disease
True positive / (True positive + False positive)
Define Negative Predictive Value (NPV) and how is it calculated?
Proportion of people with a negative test result who actually do not have the disease
True negative / (True negative + False negative)
What is lead time bias?
When screening identifies an outcome earlier than it would be otherwise have been identifies resulting in an apparent increase in survival time even if screening has no effect on outcome
What is length time bias?
Type of 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
Define primary prevention
Preventing disease form occurring int he first place
- Often eliminating risk factors that contribute to the disease
Give an example of primary prevention
- Immunisations
- Change4life
- 5 a day
Define secondary prevention
Catching a disease in its early pre clinical phase in order to alter its course and to improve health outcomes
Give an example of secondary prevention
Screening –> cervical and Breast
Define tertiary prevention
Trying to slow down disease progression, preventing complication fo the disease and helping people manage their illness effectively
Give an example of tertiary prevention
- Diabetes manages –> diet advice, exercise programmes, annual foot check
- Attending physio/rehab after a stroke to prevent immobility and aspiration pneumonia
What is the population approach to prevention?
Give an example
Preventative measures delivered on a population wide basis
E.g. Dietary salt reduction
What is the high risk approach to prevention?
Give an example
Approach
Identifying individuals above a chosen cut off and treating them
E.g. Treating those with high cholesterol to avoid heart disease
Describe the prevention paradox
A preventative measure that brings much benefit to the population often offers little to each participating individual
What are the 4 main determinants of health?
- Genes –> age, sex, genetic factors
- Environment –> Physical, socioeconomic
- Lifestyle –> smoking, exercise, alcohol, diet
- Healthcare
Wider determinants = inequalities in health, primary, secondary and tertiary prevention
What are the structural determinants of health?
Socio-economic connect that someone is born into
- Governance
- Policies
- Social and cultural values communities place on health
What factors determine someones socioeconomic position in society?
- Education
- Occupation
- Income
- Gender
- Ethnicity
- Social Class
What are the intermediately determinants of health?
- Material circumstances –> housing, clothing, food
- Psychosocial factors –> living circumstances, relationships, support
- Behavioural and biological factors
Define Equality and Equity
Equality = equal shares Equity = What is fair and just
Define horizontal equity
Equal treatment for equal need
- Individuals with same disease should all be treated equally
Define Vertical equity
Unequal treatment for unequal need
- Individuals with common cold need different treatment to those with pneumonia
- Areas with poorer health may need higher expenditure on health services
How can vertical equity be justified?
On morally relevant factors - Need - Ability to benefit - Deservingness NOT morally irrelevant factors - Age/sex - Ethnicity - Income, class - Disability, genetics
How can health equity be classified?
- Spatial –> geographical
2. Social –> age, gender, class, ethnicity
How can we examine health equity?
- Supply of healthcare
- Access to healthcare
- Utilisation of healthcare
- Health care outcomes
- Health status
- Resource allocation –> health services, education, housing
- Wider determinants of health –> diet, smoking, healthcare seeking behaviours, socioeconomic and physical environment
What are the 3 domains of public health practice?
- Health Improvement
- Health Protection
- Healthcare (Improving services)
What is meant by health improvement domain?
Concerned with societal intervention aimed at preventing disease, promoting health and reduction inequalities
Give 2 examples of the health improvement domain
- Addressing inequalities
- Education
- Housing
- Employment
- Lifestyle
- Family/community
What is meant by health protection domain?
Concerned with measures to control infectious disease risks and environmental hazards
Give 2 examples of the health protection domain
- Infectious disease
- Chemical and poisons
- Radiation
- Emergency response
- Environmental health
- Hazards
What is meant by health care domain?
Organised and delivery of safe, high quality services for prevention, treatment and care
Give 2 examples of the health care domain
- Clinical effectiveness
- Efficiency
- Service planning
- Audit and evaluation
- Clinical governance
- Equity
What are the 3 levels that a public health intervention can occur at?
- Individual level
- Community level
- Ecological (population level)
Give an example of an individual level public health intervention
Childhood immunisations –> where injection are delivered to each individual child to stop them getting ill
Give an example of a community level public health intervention
Similar to ecological level intervention but delivered at the local or community level
E.g. Playground set up for local community, more cycle paths, outdoor gym
Give an example of an ecological level public health intervention
- Clean air act –> legislation to ban smoking in enclosed public places
- Sugar tax
- Putting iodine in salt –> prevent iodine deficiency
- Screening programmes
- PH campaigns –> change4life, Movember
Define health psychology
Emphasises the role of psychological factors in the cause, progression and consequences of health and illness and promotes healthy behaviours and prevents illness
What are the 3 behaviours related to health?
- Health behaviour
- Illness behaviour
- Sick role behaviour
Define health behaviour
A behaviour aimed at preventing a disease
- Can be health damaging or health promoting
What are health damaging behaviours?
Often related to mortality
- Smoking
- Alcohol
- Substance misuse
- Sun exposure
- Driving with no seatbelt
Give 2 reasons why people engage in health damaging behaviours
- Unrealistic optimism
- Health beliefs
- Situational rationality
- Culture variability
- Socio-economic factors
- Stress
What are health promoting behaviours?
Behaviours that seek and maintain health
- Exercise
- Health eating
- Attending health check
- Medication compliance
- Vaccinations
Define Illness behaviour
A behaviour aimed to seek remedy
- Going to the doctor