Define disease
Symptoms, signs, diagnosis; a bio-medical perspective
Define illness
Ideas, concerns, expectations; experience of patients (their perspective)
What are the medical factors which affect the uptake of care (going to get care)?
New symptoms, visible symptoms, increasing severity, duration etc
What are the non-medical factors which affect the uptake of care (going to get care)?
Crisis, peer pressure “wife sent me”, patient beliefs, expectations, social class, economic, psychological, environmental, cultural, ethnic, age, gender, media etc
What is the Lays Referral concept of the uptake of care?
Going from family → community → traditional/cultural healing → medical system
Where can people get info which influences their decision for uptake of care?
Peers, family, internet TV, health pages of newspaper or women’s mag, “What should I do? Booklet, SHOW website, Practice leaflet or website
What are the three main aims of epidemiology?
- Description
- Explanation
- Disease control
Define description in epidemiology
To describe the amount and distribution of disease in human populations
Define explanation in epidemiology
Elucidate natural history and aetiology of disease by combining data from epidemiology with data from biochem/occupational health/genetics
Define disease control in epidemiology
Provide bases for preventative measures/public health practices/therapeutic strategy for disease control
What is epidemiology used for?
Compares groups to detect difference in:
Aetiology
Scope for prevention
Identify high risk group
What are the fundamental measures?
Clinical medicine deals with the individual patient and epidemiology deals with populations.
Rates: numerator = events and denominator = population at risk
What is the risk part of formulating ratios in fundamental measures?
Everyone in the denominator must have possibility of entering the numerator, and vice versa.
What does incidence indicate about a disease?
It is the number of new cases of a disease in a population in a specified period of time. Incidence tells us something about trends in causation and the aetiology of disease.
What does prevalence indicated about a disease?
It is the number of people in a population with a specific disease at a single point in time or in a defined period of time.
Prevalence tells us something about the amount of disease in a population. It is useful in assessing the workload for the health service but is less useful in studying the causes of disease.
What is relative risk?
Measure of the strength of an association between a suspected risk factor and the disease under study.
What is the equation to work out relative risk?
(Incidence of disease in exposed group) / (incidence of disease in unexposed group)
Give four examples of sources of epidemiological data
Mortality data
Hospital activity statistics
Reproductive health statistics
Cancer statistics
What is health literacy?
People having the knowledge, skills, understanding and confidence to use health information, to be active partners in their care, and to navigate health and social care systems.
Name an initiative in Scotland to improve health literacy
Making It Easy - A Healthy Literacy Action Plan
What are the SIGN guidelines aims?
Aid in understanding and help make clinical decisions
Reduce variations in practice and provide best care no matter where Pt is
Improve healthcare across Scotland
What are the two types of studies?
Descriptive and analytical
What are descriptive studies?
Describe amount and distribution of disease in a given population
- No definitive conclusions, does give clue to risk factors and aetiology
- Cheap, quick, overview
What are analytic studies?
Two types: Cross sectional (disease frequency/survey): observations in a point in time
Case Control: comparison of 2 groups
- Pt with the disease (cases)
- Pt who do not have disease (controls)
These results are compared to highlight factors on risk of disease
How are the cases and control compared in analytical studies?
The average exposure to aetiological factors of each group compared to identify significant differences which indicates which factors increase (or reduce) risk of disease
What are the result from case studies in analytical studies expressed as?
‘Odds ratios’ or ‘relative risk’
What are cohort studies?
Baseline data on a group without disease, who are then followed until disease developed enough to allow analysis
How are cohort studies analysed?
Original group separated into subgroups according to original exposure status and these subgroup are compared to determine incidence of disease according to exposure
What are trials?
Trials are experiments used to test ideas about aetiology or to evaluate interventions.
What is the definitive method of assessing any new treatment?
Randomised controlled trial
How are randomised controlled trials carried out?
- At risk groups; a study group and a control group.
- Alteration made to the study group only
- Data collected same way
What is the aim of randomised controlled trials?
Determine whether modification of the factor (changing the exposure) alters the incidence of the disease
How is a trial of a new treatment carried out?
Intervention group receive the new therapy, the control group receive the current standard therapy (or placebo) and treatment outcomes compared in two groups
What are six factors to consider when interpreting results?
- Standardisation
- Standardised mortality ratio
- Quality of data
- Case definition
- Coding and classification
- Ascertainment
What are standardisation factors to consider?
Adjusting for effects of differences of cofounding variable (i.e. age)
What is standardised mortality ratio?
Standardised death rate converted to ratio, e.g. standard is 100, 120 means 20% more death than expected
What is the factor ‘case definition’?
Decide if an individual has the condition of interest or not; varying definition from study maker to interpreter
What is the factor ‘coding and classification’?
When data collected it is converted to a set of codes, to assist in data storage and analysis
What is the factor ‘ascertainment’?
Completeness of data. One group looking harder than another
What is bias?
Trend in the collection, analysis, interpretation, publication or review of data that can lead to conclusions that are systematically different from the truth.
What are four different types of bias?
Selection Bias
Information Bias
Follow up Bias
Systematic Error
Define selection bias
Study sample is not truly representative of the whole study population about which conclusions are to be drawn
Define information bias
Arises from systematic errors in measuring exposure or disease
Define follow up bias
Arises when one group of subjects is followed up more assiduously than another
Define systematic error
A form of measurement bias where there is a tendency for measurements to always fall on one side of the true value
May be caused by:
Instrument
Wrong technique
Define a cofounding factor
Associated independently with both the disease and with the exposure under investigation and so distorts the relationship between the exposure and disease.
Age, sex and social class
Name ways to deal with a cofounding factor
Restriction eligibility criteria
Subjects in different group can be matched for likely cofounding factors
Results adjusted
What are the 9 criteria for causality
Temporality: exposure comes before disease [only absolute criterion]
Strength of association: relative risk ratio
Consistency: repeated observation of association in differing populations
Specificity: single exposure leads to single disease
Biological gradient: dose
response relationship i.e. exposure UP = risk UP
Biological plausibility: association agrees with biology of disease
Coherence: association does not conflict with biology of disease
Analogy: another relationship exists that can be used as a model for current
Experiment: suitably controlled experiment to prove association as causal(uncommon in human populations)
