Epidemiology Flashcards
Causality
Multifactorial aetiology
Despite cases of a “link”, still many other factors like genetics, behavioural, social, domestic.
Occupational diseases
Factors in the work environment are predominant and essential in causation
Work Related Diseases
Can also occur outside the work place.
Partially caused by adverse working conditions
Point prevalence
Rate of a disease is the proportion of the population at risk who are affected at a GIVEN TIME
Incidence
Rate of disease refers to NEW CASES only.
Defined as proportion of the population at risk who DEVELOP the condition within a stated time period.
Indicates risk of contracting the disease.
Prevalence
Proportion of cases in a population at a given time. Indicates how widespread the disease is.
Prevalence = Incidence x average duration
This depends partly on the rate at which new cases occur (incidence) and on duration
Incidence vs Prevalence
Incidence is preferred but are more difficult to estimate.
Relative Risk
The ratio of incidence of a disease in an exposed population to the incidence in an unexposed population
In Cohort Studies.
Incidence in exposed group/Incidence in non exposed group
Cohort Study
Prospective Study in general
Measures Relative Risk
Observe one or more defined population over a period of time starting in past or present. Identify all that become sick or die (incident cases) and those who do not.
Case Control Study (Case referent)
Retrospective
Odds Ratio
Select a series of cases of the disease of concern and a series of people without the disease but of the same population.
Then compare exposure history of 2 groups
Measures incidence as over time.
Not as effective as Cohort
Cross Sectional Study
(Prevalence Study) - Cannot measure incidence
Measured at a particular point in time (not longitudinal)
This is often used on current employees in Occy setting
Best for rare diseases
Case control
Best for latency
Cohort
Is most expensive
Recall Bias
Can occur if occupational histories of cases are more or less complete/accurate than those of non cases.
Those with negative affect are more likely to remember exposure history.
A form of information bias
Confounding
Where the measured effect of one agent is distorted by the effect of others.
The other agent is the confounder.
EG. relationship between oral cancer and ETOH
But more smokers in drinking group (tobacco is the confounder)
Period Prevalence
Proportion of a population who have a disease over a defined period.
Direct Standardization
Simply a weighted average of sex and age specific rates
Indirect Standardization
Comparison of observed cases of disease to expected cases of disease
Odds Ratio
Odds of disease in a person exposed to a risk factor divided by the odds in someone who is unexposed.
Experimental Studies
Assess the effect of a planned intervention on outcomes of interest.
Hawthorne Effect
Those studied act differently because they are being studied.
Form of information bias
Selection Bias
Healthy worker effect
Self selection
Information bias
Hawthorne effect
Recall bias
Healthy Worker Effect
Those that do an arduous manual job are likely to healthier than those that do not.
Self Selection
Those who chose to take part in studies may be different to the general population (they may be healthier, more likely to be exposed to a substance)
Type 1 Error
False Positive
Type 2 Error
False Negative
Attributable Risk
Number of cases with a disease attributed to an exposure.
RISK DIFFERENCE - Risk in exposed group minus risk in non exposed group.
Sensitivity
Percentage of true positives in a sample
Specificity
Percentage of true negatives
Bradford Hill Criteria
Set of nine criteria to provide epidemiologic evidence of a causal relationship.
Specificity is included, sensitivity is NOT.
Synergisitc
It works together to increase the effect.
It produces a combined effect greater than the sum of their separate effects.
p value
Aim to be as low as possible <0.05
If so suggests study is statistically valid.
RR Values
RR = 1 No diff between exposed and non exposed group
RR >1 Increased risk of outcome in exposed group
RR<1 Decreased risk of outcome in exposed group
