Flashcards in Epidemiology Deck (49)
What is epidemiology?
The study of the occurrence and distribution of health-related events in specified populations, including the study of the determinants influencing such states and the application of this knowledge to control the health problems
What is descriptive epidemiology?
describing patterns of health and disease in populations
What is analytical epidemiology?
Identifying why some populations or individuals are at greater risk of disease and hence identify the risk factors
Give the PICO process
P – patient, problem or population (What is the problem to address? Identification of the target population)
I – intervention (Risk factor under investigation)
C – comparison, control or comparator
O – outcome (Disease/Health state)
Define the term 'ecological study'
An observational study where the exposure and/ or disease is observed at a group level. The group is the unit of observation e.g. the group may be defined as hospital/ health region etc.
Define the term 'cross sectional study'
A snapshot of the frequency of diseases and exposures in a particular population at a specific time-point.
Define the term 'cohort study'
An observational study which identifies a group of people and follows them over a period of time to determine incidence of, or mortality from, specific disease(s) and see how their exposures affect their outcomes.
What are case control studies?
A retrospective study which compares how frequently the exposure to a risk factor is present in a group of individuals who have a specific disease (case) and in another group of individuals without the disease (control)
What's the problem with observational studies?
Multiple factors can contribute to a disease and some factors only have an indirect relation to the disease. In observational studies, we only observe. There's no control on who is exposed, what, how, when.
Define the term 'randomised controlled trial'
A study in which a number of similar people from a target population are randomly assigned to 2 or more groups to test a specific drug, treatment or other intervention.
Why are RCTs the gold standard for research?
Randomisation allows to create two comparable groups with the exception of the received treatment.
Control of potential confounders and other influential factors as two groups equally affected.
No selection bias induced by the recruiter to favour one treatment over the other
Why is epidemiology important in making public health decisions?
Epidemiological studies show what's healthy/unhealthy, which then influence government policy
What are in vivo studies?
Studies done in living organisms
What are in vitro studies?
Studies performed or taking place in a test tube, culture dish, or elsewhere outside a living organism.
Why are in vivo and in vitro studies limited?
The effects shown in animals are possibly different to the effect in humans
Cells behave differently outside the body compared to within the body
Strengths of case-control studies
Good quality data as it was collected specifically for the study
Relatively quick and cheap to conduct- no long periods of follow up
Can study multiple exposures and outcomes
Efficient for rare outcomes
Weaknesses of case-control studies
Temporal sequence is unknown (can't be sure if exposure came before outcome)
Prone to bias, both selection and measurement
Confounding factors that are related to exposure and outcome that explain the association
Can not calculate incidence rates
Inefficient for rare exposures
Define the term 'confounder'
A confounder (also confounding variable, confounding factor or lurking variable) is a variable that influences both the dependent variable and independent variable causing a spurious association.
Define the term 'mediator'
A mediator is a variable that causes mediation in the dependent and the independent variables. In other words, it explains the relationship between the dependent variable and the independent variable.
Describe experimental design studies
Full control of who is exposed, and of the different exposure factors (observed or not).
Describe observational design studies
Exposure are not assigned by the researcher, only the observed exposure can be investigated, no control on the unobserved exposure.
What are cases in case-control studies?
Someone with the thing that you're investigating
What are controls in case-control studies?
Individuals who would have been cases if they had developed the outcome
An odds ratio (OR) is a measure of association between an exposure and an outcome.
The OR represents the odds that an outcome will occur given a particular exposure, compared to the odds of the outcome occurring in the absence of that exposure.
What does an OR value of 1 mean?
There's no difference between exposure groups
What does an OR value of <1 mean?
Exposure reduces the odds of the outcome developing
What does an OR value of >1 mean?
Exposure increases the odds of the outcome developing
What does representativeness mean?
How representative is the selected sample of the target population?
(can use response rate as a guide)
What does generalisabilty mean?
How generalisable are the results based on the selected sample (which should represent the target population) to other populations?
List some features of cross-sectional studies
A defined population of interest
A representative sample of individuals
Surveyed at a particular point in time
Obtain simultaneously information on both the outcome of interest and exposure(s)
Strengths of cross-sectional studies
Good quality data as collected for the purpose of research (i.e. not from routine data collections)
Relatively quick and cheap to conduct (no long periods of follow up)
Can study multiple exposures and outcomes
Weaknesses of cross-sectional studies
Temporal sequence unknown
- can not be sure exposure came before outcome
Prone to bias (selection and measurement)
What is meant by regression in statistics?
A measure of the relation between the mean value of one variable (e.g. output) and corresponding values of other variables (e.g. time and cost).
Why are regression models used?
Regression can be used to assess the strength of association between an exposure and outcome.
Multiple regression can be used to assess the strength of association between an exposure and outcome after adjustment for confounders
Risk ratio is the ratio of the probability of an event occurring (for example, developing a disease, being injured) in an exposed group to the probability of the event occurring in a comparison, non-exposed group.
What's the difference between an odds ratio and a risk ratio?
An odds ratio is simply an association. That is to say what are the "odds" of having one condition or exposure if you have another- the two conditions are statistically significantly related. Risk ratio is generally considered as the risk of developing one condition if you have the exposure as compared to another group of differing exposure.
Strengths of RCTs
Direct comparison of treatments
Can make causal inference
Randomisation minimises bias
Randomisation minimises confounding
Statistical test of significance is easily interpretable
If sufficient power, avoids Type 1 and Type 2 errors
Weaknesses of RCTs
If large sample size required (e.g. small effect, rare outcomes), very expensive & logistically difficult
If outcomes occur after long delay, increases costs and loss to follow up
Results may not be achieved in “real life” outside study
Ethical implications – RCT not possible without clinical equipoise
Informed consent may be impossible
What is clinical equipoise?
Genuine clinical uncertainty between 2 options
Purpose of epidemiology
The ultimate purpose of epidemiology is prevention of diseases and promotion of health
How does epidemiology prevent diseases and promote health?
1. Clarification of natural history of diseases
2. Description of health status of population
3. Establishing determinants of diseases
4. Evaluation of intervention effectiveness
What are the basic epidemiological assumptions?
1. Human diseases doesn’t occur at random or by chance
2. Human diseases have causal and preventive factors
List the three major levels of disease prevention
Targeted at healthy people
Objectives are the promotion of health, prevention of exposure and prevention of disease
Targeted at sick individuals
Objective is to stop or slow the progression of disease and to prevent or limit permanent damage through early detection & treatment.
Targeted at people with chronic diseases & disabilities that can’t be cured
Objective is to prevent further disability or death and to limit impacts of disability through rehabilitation
What is a disease reservoir?
An organism or habitat in which an infectious agent normally lives, transforms, develops and/or multiplies
What is a disease carrier?
A person who doesn’t have apparent clinical disease, but is a potential source of infection to other people