1. 2017/2018

2. Public Health Phase 3a Revision Session Katie Newton and Heidi Coombes
2nd November 2017
BOTH
Intro – explain Katie doing MPH
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3. Session Contents Domains of Public Health Health Inequality
Study Design and Interpretation
Incidence/prevalence and calculations
Interpreting Association
Health Needs Assessments
Health Psychology and Behaviour Change
Communicable Disease Control
HEIDI
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4. Domains of Public Health
What are the three domains of public health?
Health improvement
Health protection
Improving services
Can you give examples of these?
HEIDI
Health improvement
Inequalities
Education
Housing
Employment
Lifestyles
Family/community
Health protection
Infectious disease
Chemicals and poisons
Radiation
Emergency response
Environmental health hazards
Health care
Clinical effectiveness
Efficiency
Service planning
Audit and evaluation
Clinical governance
equity
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5. Health Inequality What influences health inequalities?
What is the difference between equality and equity?
Equity – giving everyone what they need to be successful
Equality – treating everyone the same
HEIDI
PROGRESS:
Place of Residence (rural, urban, etc.)
Race or ethnicity
Occupation
Gender
Religion
Education
Socioeconomic status
Social capital or resources
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6. Horizontal vs Vertical Equity
Horizontal equity
“equal treatment for equal need”
Vertical equity
“unequal treatment for unequal need”
HEIDI
e.g. horizontal – all people with pneumonia deserve equal treatment, all else being equal
e.g. vertical – individuals with pnuemonia deserve different treatment from those with common cold
e.g. vertical – areas with poorer health may need higher expenditure on health services
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7. Study Design What is a cohort study? Advantages of cohort study?
Longitudinal study in similar groups but with different risk factors/treatments.
Follows up over time
Advantages of cohort study?
Can follow up rare exposure
Allows to identify risk factors
Data on confounders collected prospectively
Disadvantages of cohort study?
Large sample size required
Impractical for rare diseases
Expensive People drop out
HEIDI
What is a cohort study?
Longitudinal study in similar groups but with different risk factors/treatments.
Follows up over time
Advantages of cohort study?
Can follow up rare exposure
Allows to identify risk factors
Data on confounders collected prospectively
Disadvantages of cohort study?
Large sample size required
Impractical for rare diseases
Expensive People drop out
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8. Study Design What is a case control study? Advantages of case control?
Observational study looking at cause of a disease.
Compares similar participants with disease and controls without
Looks retrospectively for exposure/cause
Advantages of case control?
Quick
Good for rare outcomes
Disadvantages of case control?
Difficult finding appropriately matched controls
Prone to selection and information bias
HEIDI
What is a case control study?
Observational study looking at cause of a disease.
Compares similar participants with disease and controls without
Looks retrospectively for exposure/cause
Advantages of case control?
Quick
Good for rare outcomes
Disadvantages of case control?
Difficult finding appropriately matched controls
Prone to selection and information bias
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9. Study Design What is a cross sectional study?
Observational study collecting data from a population and a specific point in time
A snapshot of a group
Advantages of cross sectional?
Large sample size
Provides data on prevalence of risk factors and disease
Quick to carry out
Repeated studies show changes over time
Disadvantages of cross sectional?
Risk of reverse causality – which came first?
Less likely to include those who recover quickly or short recovery
Not useful for rare outcomes
HEIDI
What is a cross sectional study?
Observational study collecting data from a population and a specific point in time
A snapshot of a group
Advantages of cross sectional?
Large sample size
Provides data on prevalence of risk factors and disease
Quick to carry out
Repeated studies show changes over time
Disadvantages of cross sectional?
Risk of reverse causality – which came first?
Less likely to include those who recover quickly or short recovery
Not useful for rare outcomes
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10. Study Design What is a randomised controlled trial?
Similar participants are randomly assigned to an intervention or control group to study effect of intervention
What are the advantages of RCT?
Low risk of bias and confounding
Comparative
What are the disadvantages of RCT?
High group out rate
Ethical issues
Time consuming and expensive
HEIDI
Causal differences: Can show the effect is due to the intervention
Low risk of bias and confounding
Study tailored to answer specific research question
High drop out rate, little incentive to stay in control arm
Ethical issues
Prior knowledge required
Time consuming and expensive
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11. Incidence and prevalence
What is the difference between incidence and prevalence?
HEIDI
Incidence- Number of new cases in a population during a specific time period.
Prevalence- Number of existing cases at a specific point in time
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12. Incidence
Over a ten year period, there were 50 new cases of lung cancer in Crookes (a population of 1,000 people).
What is the incidence of lung cancer over those 10 years?
50/1000 = 5%
HEIDI
Answer = 5%
Incidence- Number of new cases in a population during a specific time period.
Prevalence- Number of existing cases at a specific point in time
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13. Comparing Incidence
In Crookes (population of 1000 people), 300 of them smoke. Of those who smoke, 45 of them developed lung cancer. 5 of the non-smokers developed lung cancer.
What is the relative risk of lung cancer in smokers?
Risk of lung cancer in smokers = 45/300 = 15%
Risk of lung cancer in non-smokers = 5/700 = 0.7%
Relative risk (ratio) = 15/0.7 = 21.4
So… 21.4 times more likely to develop lung cancer if smoker
HEIDI
Risk of lung cancer in smokers = 45/300 = 15%
Risk of lung cancer in non-smokers = 5/700 = 0.7%
Relative risk (ratio) = 15/0.7 = 21.4
So… 21.4 times more likely to develop lung cancer if smoker
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14. Attributable Risk
In Crookes (population of 1000 people), 300 of them smoke. Of those who smoke, 45 of them developed lung cancer. 5 of the non-smokers developed lung cancer.
What is the risk of lung cancer that is attributable to smoking?
Risk of lung cancer in smokers = 45/300 = 15%
Risk of lung cancer in non-smokers = 5/700 = 0.7%
Attributable risk (risk difference) = (15/100)-(0.7/100) = 14.3/100
HEIDI
Attributable risk = amount of lung cancer that is specifically due to smoking. So if you think about it, you need to take away the “naturally occuring” cases that “would have happened anyway”, from the number of cases in the exposed.
Risk of lung cancer in smokers = 45/300 = 15%
Risk of lung cancer in non-smokers = 5/700 = 0.7%
Attributable risk (risk difference) = (15/100)-(0.7/100) = 14.3/100
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15. Number needed to treat
In Crookes (population of 1000 people), 300 of them smoke. Of those who smoke, 45 of them developed lung cancer. 5 of the non-smokers developed lung cancer.
How many people would have to give up smoking to prevent one death from lung cancer?
Attributable risk = 0.143
NNT = 1/attributable risk = 1/0.143 = 6.99
HEIDI
Attributable risk = 0.143
NNT = 1/attributable risk = 1/0.143 = 6.99
So if 7 people gave up smoking in this population, you would prevent one death from lung cancer. Always round up a number needed to treat, as you can’t treat a fraction of a person.
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16. Sensitivity and Specificity (Screening)
Positive predictive value =
Negative predictive value:
Pos PV
= a / a + b
= TP / (TP + FP)
Neg PV
= d / (c + d)
= TN / (FN + TN)
HEIDI
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17. Sensitivity and Specificity (Screening)
Sensitivity = % correctly identified with the disease
Specificity = % correctly excluded as disease free
Pos PV
= a / a + b
= TP / (TP + FP)
Neg PV
= d / (c + d)
= TN / (FN + TN)
HEIDI
100% sensitive correctly identifies everyone with the disease as having the disease, but may cause false positives
Can be calculated from the number of true positives over everyone screened with the disease
100% specific correctly excludes everyone without the disease, but may miss people who do have the disease
Can be calculated from the number of true negatives over everyone who does not have the test
Positive predictive value= % of those with a positive test that actually have the disease
Negative predictive value= % of those with a negative test who are actually disease free
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18. Make sure you know screening criteria:
Important disease
Natural history of the disease must be understood e.g. detectable risk factors, disease marker
Simple, safe, precise and validated test
Acceptable to the population
Effective treatment from early detection with better outcomes than late detection
Policy of who should receive treatment
HEIDI
Important disease
Natural history of the disease must be understood e.g. detectable risk factors, disease marker
Simple, safe, precise and validated test
Acceptable to the population
Effective treatment from early detection with better outcomes than late detection
Policy of who should receive treatment
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19. Interpreting Association
What can association be due to?
Bias
Chance
Confounding
Reverse Causality
True association
HEIDI
Analytical methods may confirm an association between an exposure and an outcome but causality can only be confirmed if alternative explanations are accounted for.
Bias – systematic differences between comparison groups which may misrepresent the association being investigated
Chance – possibility that there is a random error
Confounding –
Reverse Causality – outcome results in exposure
True association
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20. Bias What is bias? Three types of bias:
A systematic error that results in a deviation from the true effect of an exposure on an outcome
Three types of bias:
Selection bias
Non response of certain groups, allocation bias (different participants in different groups)
Information bias
Measurement bias, observation bias, recall bias (doesn’t remember or recall correctly), reporting bias (don’t report truth because feel judged)
Publication bias
Trials with negative results less likely to be published
HEIDI
A systematic error that results in a deviation from the true effect of an exposure on an outcome
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21. Bias What is the difference between lead time and length time bias?
HEIDI
Lead time bias= Early identification doesn’t alter outcome but appears to increase survival
e.g. patient knows they have the disease for longer
Length time bias= Disease that progress more slowly is more likely to be picked up by screening (i.e. symptom free and around for longer), which makes it appear that screening prolongs life.
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22. Confounders What is confounding? HEIDI
Exposure – having grey hair associated with back pain
When an apparent association between an exposure and an outcome is actually the result of another factor.
Other factors that influence the outcome and ‘explain why’ some of the relationship between exposure and outcome
Another example: study looking at association between occupation and lung cancer could be the result of the occupational cohort more likely to smoke and therefore at increased risk
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23. Causation What are the Bradford Hill Criteria for causation?
Temporality
Dose-response
Strength
Reversibility
Consistency
There are others…
HEIDI
Bradford hill listed nine considerations that are used in epidemiology to build up evidence for a causal relationship.
Strength - very high relative risk (Relative Risk of 21) – the stronger the association between the exposure and outcome, the less likely that the relationship is due to some other factor
Temporality - most important - exposure occurs before outcome (people smoke before developing lung cancer)
Dose-response - more risk of outcome with more exposure (the more you smoke the higher the risk of lung cancer)
Reversibility - if you take away the exposure then the risk of disease decreases or is eliminated (stop smoking and you have a decreased risk of lung cancer after 10 years or so)
Consistency - the association is seen in different geographical areas, using different study designs, in different subjects (smoking is associated with lung cancer in dogs, mice and people, all over the world). Repeatability of the result.
Plausability – existence of reasonable biological mechanism for the cause and effect lends weight to the association
Coherence – logical consistency with other information
Analogy - similarity with other established cause effect relationships
Specificity – the relationship being specific to the outcome of interest
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24. Health Needs Assessments
What are the stages of the “planning cycle” for health services? ?
KATIE
Needs assessment – planning – implementation – evaluation
Health needs assessments are the first stage of the “planning cycle” for health services – this cycle is the process that all health services go through for improvements, new services etc.
Definition - HNA provides a systematic approach to assessing health needs to reduce inequalities in health and inform decision making and action planning to improve health.
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25. Health Needs Assessments
What are the stages of the “planning cycle” for health services?
Needs Assessment
Planning
Implementation
Evaluation
KATIE
Needs assessment – planning – implementation – evaluation
Let’s break HNA into it’s different components
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26. Health Needs Assessments
How do we define ‘health’?
Bio-medical
Absence of disease
Psychosocial
Stress and function
Lay views
Felt and expressed needs
KATIE
The definition of health used / who defines health is the first step in carrying out a HNA
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27. Bradshaw’s ‘Needs’ - ? KATIE
Next we need to think about which Needs we’re assessing – commonly use Bradshaw’s needs:
Felt needs
Expressed needs
Normative needs
Comparative needs
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28. Bradshaw’s ‘Needs’ - Felt need Expressed need Normative need
Comparative need
Can you define them?
KATIE
Felt need – individual perceptions of variation from normal health
Expressed need – individual seeks help to overcome variation in normal health (demand)
Normative need – professional defines intervention appropriate for the expressed need
Comparative need – comparison between severity, range of interventions and cost
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29. Three approaches to an HNA?
KATIE
Finally – the assessment itself – there are 3 core different ‘approaches’ to an HNA
Epidemiological
Comparative
Corporate approach
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30. Three approaches to an HNA
Epidemiological approach
Comparative approach
Corporate approach
Can you explain each one?
Can you discuss advantages/disadvantages of each?
KATIE
Epidemiological approach:
Very top down
Define your issue, assess the size of it (incidence/prevalence), assess the services available for this issue, assess if this is matching the evidence base for effectiveness and cost-effectiveness, assess the care (using quality and outcome measures e.g. QOF) and assess for any unmet need and any unneeded services - using all of this, make recommendations
Problems with this – data – may not be available/high quality, doesn’t consider felt needs, reinforces biomedical approach
Comparative approach:
Basically you take two populations/areas and compare the services received by one of them, with another – fairly quick and cheap, and can measure the variation
Problems – data not available/high quality, difficulties finding a comparable group, and also it’s possible that neither group is using the ideal services! No assessment against current evidence.
Corporate approach:
Collect the views of the “stake holders” e.g. The patients/service users, GPs, other health professionals etc – ask them what they think is needed.
Problems – blurs the difference between need and demand. Vulnerable to influence by political and personal views etc.
Is everyone happy with HNAs?
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31. Models of behaviour change?
How many can you name?
KATIE
Moving on now to some health psych – main thing covered for 3a was behaviour change and different models for this.
There’s about 8 discussed in 3a, but only 3 key ones – how many can you name?
Health Belief Model
Theory of Planned Behaviour
Stages of Change/Transtheoretical Model
Social norms theory
Motivational Interviewing
Social Marketing
Nudging
Financial Incentives
There’s more out there if you’re interested
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32. Models of behaviour change
Health Belief Model
Theory of Planned Behaviour
Stages of Change/Transtheoretical Model
Social norms theory
Motivational Interviewing
Social Marketing
Nudging
Financial Incentives
KATIE
First 3 are the main three discussed in 3a teaching, so the ones most likely to come up!
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33. Chance of engaging in health-promoting behaviour
Health Belief Model
Chance of engaging in health-promoting behaviour
Perceived ?
KATIE
This model is focused around the idea that to increase the chance of an individual changing a health behaviour, you need to influence how they perceive these 4 factors.
… susceptibility to ill health
… severity of ill health
… benefits of behaviour change
… barriers to taking action
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34. Health Belief Model Perceived susceptibility to ill health
Chance of engaging in health-promoting behaviour
Perceived susceptibility to ill health
Perceived severity of ill health
Perceived benefits of behaviour change
Perceived barriers to taking action
KATIE
So e.g. for smoking cessation – they need to perceive that they could get lung cancer, that lung cancer is bad for them, that by stopping smoking they will reduce their risk of lung cancer/cough less etc, and the there are smoking cessation services to help them remove the barriers
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35. Stages of change/trans-theoretical model
Pre-contemplation ?
Maintenance
KATIE
This is the model we’re all most familiar with.
Basically argues that there are 5 core stages of behaviour change, and that there’s fluid movement between them – i.e. you work your way along the steps at your own pace, but at any point a relapse may send you back to the start.
Pre-contemplation
Contemplation
Preparation
Action
Maintenance
Relapse
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36. Stages of change/trans-theoretical model
Pre-contemplation
Contemplation
Preparation
Action
Maintenance
KATIE
e.g. smoking cessation
Pre-contemplation – not considered quitting
Contemplation – thinking about quitting
Preparation – buying NRT patches, setting quit date
Action - quitting
Maintenance – remaining a non-smoker
Relapse
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37. Perceived behavioural control
Theory of planned behaviour
Attitudes
Subjective norm
Intention
Behaviour
KATIE
Basically says that different things come together to give someone the intention to change, and once they decide to change, they will. – puts everything on the idea of ‘planned behaviour’ being the actual behaviour.
Attitudes – believing that smoking is bad for you
Subjective norm – difference between thinking oh everyone smokes to actually not many people smoke
Perceived behavioural control – thinking that they are in control of their smoking, that if they want to quit they will be able to
Perceived behavioural control
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38. Communicable Disease Control
What are the features of a communicable disease that would make it a public health concern?
High mortality
High morbidity
Highly contagious
Expensive to treat
Effective interventions
KATIE
CDC plays a big part in public health.
High mortality
High morbidity
Highly contagious
Expensive to treat
Effective interventions
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39. Communicable Disease Control
Notifiable Diseases
Who?
When?
What?
How?
KATIE
The key things to know about notifiable diseases is –
Who
When
What
How
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40. Communicable Disease Control
Notifiable Diseases
Who?
Registered medical practitioners
Labs
When?
Any case of a notifiable disease – on clinical suspicion! Not lab confirmation.
Any other infection/contamination that could risk human health
KATIE
Who?
Registered medical practitioners
Labs
When?
Any case of a notifiable disease – on clinical suspicion! Not lab confirmation.
Any other infection/contamination that could risk human health
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41. Communicable Disease Control
Notifiable Diseases
What?
Case details e.g. NHS no., DOB, contact details
Details of the disease/contamination
How?
Contact local health protection authority / PHE
Written notification or telephone if urgent
Might be worth going over the list of notifiable diseases – can be easy marks!
KATIE
What?
Case details e.g. NHS no., DOB, contact details
Details of the disease/contamination
How?
Contact local health protection authority / PHE
Written notification or telephone if urgent
List:
Acute encephalitis
Acute infectious hepatitis
Acute meningitis
Acute poliomyelitis
Anthrax
Botulism
Brucellosis
Cholera
Diphtheria
Enteric fever (typhoid or paratyphoid fever)
Food poisoning
Haemolytic uraemic syndrome (HUS)
Infectious bloody diarrhoea
Invasive group A streptococcal disease
Legionnaires’ disease
Leprosy
Malaria
Measles
Meningococcal septicaemia
Mumps
Plague
Rabies
Rubella
Severe Acute Respiratory Syndrome (SARS)
Scarlet fever
Smallpox
Tetanus
Tuberculosis
Typhus
Viral haemorrhagic fever (VHF)
Whooping cough
Yellow fever
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42. Some quick definitions
Cluster
Suspected outbreak
Confirmed outbreak
Epidemic
Pandemic
Endemic
Hyper-endemic
KATIE
Cluster = An aggregation of cases which may or may not be linked
Suspected outbreak = Occurrence of more cases than normally expected within a specific place/ group over a given period of time. 2+ cases linked through common exposure/ characteristic/ time/ location . SINGLE case of rare/ serious disease
Confirmed outbreak = Link confirmed through epidemiological/ microbiological investigation
Epidemic = Occurrence within an area in excess of what is expected for a given time period
Pandemic = Epidemic widespread over several countries
Endemic = Persistent level of disease occurrence
Hyper-endemic = Persistently high level of disease occurrence
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43. Exam Questions
Explain the difference between secondary and tertiary prevention
Explain the difference between horizontal and vertical equity in relation to health care
KATIE
Secondary prevention includes interventions aimed at early detection and treatment, such as screening, and those aimed at minimising the effect of a health event that has occurred (e.g. aspirin after an MI, mammography screening to detect early stage breast cancer), while tertiary prevention is about preventing worsening symptoms and complications of an existing disease e.g. cardiac rehabilitation, diabetic nurses)
I remember prevention by thinking of the example of trying to prevent deaths from car accidents:
Primary prevention = speed limits, preventing accidents from happening in the first place
Secondary prevention = seat belt laws, minimising risk/severity of injury when an accident occurs
Tertiary prevention = rapid response paramedics arriving early at the scene, minimising risk of death or long term disability after injury occurs
2) Horizontal equity argues that everybody with the same needs should receive the same treatment/access to health care – so two people with diabetes in two different parts of the country should receive the same level of health care. Vertical equity argues that some people have greater needs than others and so should receive unequal treatment, for example it would be equitable for someone with a chronic disease to have more GP appts than someone who is generally healthy.
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44. Exam Questions
Explain what is meant by the comparative approach to a health needs assessment
Give one health related example of something that you consider is demanded but not needed or supplied, clearly explaining the reasoning for your example
KATIE
A comparative approach to a health needs assessment involves comparing health performance across different groups e.g. different geographical areas, different disease groups, different service providers, or even the same community at different points in time. Benefits – quick and cheap, allows comparison. Disadvantages – can be hard to find the right comparator, you aren’t comparing to a gold-standard etc
E.g. antibiotics for viral illness. Patients frequently demand antibiotics for a viral cold/flu-like illness, and it is down to the practitioner to explain that this is not needed and to ensure that they aren’t supplied, in order to combat antibiotic resistance. However, in some situations this may fall into the category of demanded and supplied, but not needed.
Tip – draw a venn diagram of need, demand and supply, and try to think of any example for each combination of them e.g. needed, demanded and supplied, supplied and needed but not demanded etc – then you will easily be able to answer any version of this question in the exam!
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45. Thanks for coming! Please fill in a feedback form.
If you have any questions or
Slides will be uploaded to PTS website tonight – we have packed the ‘notes’ section with info so please have a look there if you’re stuck!
BOTH
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