Epidemiology 4 Flashcards
What is the definition of a risk factor?
- An environmental, behavioural or biological factor confirmed by temporal sequence, usually increasing the probability of a disease occurring, and, if absent or removed, reduces the probability
- Risk factors are part of the causal chain, or expose the host to the causal chain. Once disease occurs, removal of a risk factor may not result in a cure
Do diseases tend to have a single cause?
- No
- Most result from exposure of susceptible individuals to one or more causal agents
Does exposure to causal agents inevitably result in disease?
- No
What is the Bradford Hill criteria? (9)
Selected criteria for a causal association i.e. Factor under study likely to cause disease
- Strength of association
- Dose response
- Change in risk factor - reduction
- Time sequence
- Consistency
- Specificity - defined exposures
- Biological plausibility
- Experimental preventive trials
What is a ‘cause’?
- External agent which results in disease in susceptible individuals
- Not all factors associated with occurrence of disease are causes
- Some factors may be associated independently with a causal agent but do not themselves cause disease or increase risk of developing disease
What is the definition of a confounding variable?
- Particular type of extraneous variable which for some reason has been left uncontrolled. The result is that on looking at the findings of an experimental study, rather than only one possible variable exerting influence on outcome, there are found to be others, which are said to be confounding the result
What is a risk factor hypothesis?
- Suggestion that exposure to a particular agent may cause the development of a particular disease if susceptible individual is exposed to the agent in question OR
- Suggestion that possession of certain characteristics (e.g. socio-economic ststua, ethnicity, genetics) may make disease outcome more likely if exposed to certain agents
What are the three common indices of risk?
- Absolute
- Relative
- Attributable
What is absolute risk?
- Most basic measure
- Incidence rate of disease amongst people exposed to agent
- Not very useful, as assumes no risk incurred by people not exposed to agent
What is Attricutable risk?
- Difference between incidence rates and non-exposed groups
- Represents the risk attributable to factor being investigated
What is relative risk?
- Ratio of incidecne rate in exposed group to the incidence rate in non-exposed group
- Measuement of proportionate increase in disease rates of exposed group
- Makes allowance for frequency of disease amongst people not exposed to supposed harmful agent
What do analytic observational studies search for the association between?
- Search for association between factor or set of factors and a disease
- Ovservational - not experimental
- Investigator observes what is happening normally in the population
- Involves comparing disease experience of two or more groups of people in relation to their posession of certain characteristcs or exposure to a suspected factor or factors
What are analytic observational studes designed to do?
- Designed to test specific hypotheses
What is the aim of analytic observational studies?
- Aim to define risk factors of disease more precisely
What is it possible to get from the results of an analytic observational study?
- From results may be possible to suggest ways of preventing/controlling disease
