Epidemiology Flashcards
Define epidemiology, including its characteristics, aims and applications.
Epidemiology is the study of the distribution and determinants of health related events amongst a population, and the application of this study to disease prevention/control.
Distribution - frequency (counts & rates) and patterns of disease (place, person and time)
Determinants - causes and risk factors of disease
Aims include:
- describe the patterns, distribution and extent of disease amongst populations
- understand why disease is more, or less common in some groups
Applications include:
- use info to compose effective and appropriate public health interventions to prevent and control disease within the community.
Describe the various kinds of health outcomes
non-communicable disease communicable diseases birth outcomes mortality (death) morbidity (state of being unwell with a condition)
Describe the difference between:
- endemic
- epidemic
- pandemic
Endemic
- disease that is constantly present within a population
- infection rate is low
Epidemic
- outbreak (sudden increase in cases) of a disease spreading throughout a large population
Pandemic
- outbreak (sudden increase in cases) of a disease spreading across countries, continents and worldwide.
What are the three types of risk factor?
fixed marker:
- risk factor that cannot be changed e.g., gender, age, ethnicity.
causal risk factor:
- a risk factor that can be manipulated, and when manipulated, changes an outcome.
variable risk factor:
- a risk factor that can be shown to change spontaneously, or as the result of an intervention.
Describe the term ‘rates’.
Rates refers to a measure that relates the number of cases during a certain amount of time, to the size of the population.
Useful when comparing the frequency of disease in populations of different sizes.
The measurement includes incidence and prevalence of disease.
incidence: total number of new cases within a population within a specific time
prevalence: total number of cases in a population within a specific time
List some factors that can increase and decrease disease prevalence.
Increase:
- improved diagnostics
- long duration of disease
- emigration of healthy people
- immigration of infected people
- high infection rate
- increase in new cases
Decrease:
- delayed diagnostics
- short duration of disease
- emigration of infected people
- immigration of healthy people
- high fatality rate
- introduction of treatment/vaccine
Describe the difference between descriptive and analytical epidemiological study, including reference to the hierarchy of evidence.
Descriptive:
- who (person, population)
- what (clinical symptoms, disease)
- where (region, country)
- when (time frames e.g., 24 hours - 1 year)
Analytic:
- How (risk factors and aetiology of disease)
- Why (modes of transport)
Descriptive epidemiological study e.g., case report, is at the bottom of the hierarchy of evidence pyramid.
Analytic study e.g., RCT is at the top of the pyramid.
What are the two main categories of epidemiological study?
Including the various study types in each.
Observational and experimental
observational:
- cohort
- ecological
- case control
- cross sectional
experimental:
- randomised controlled trial
- non randomised controlled trial
Describe cross sectional study, including strengths and weaknesses and an example of a cross sectional study.
Cross sectional study is a snapshot of the population at a given time, examining exposure and outcome variables simultaneously.
E.g., the NDNS survey (national diet and nutrition survey).
Strengths:
- quick, easy, inexpensive
- no follow up required
- can show association between variables
Limitations:
- unable to infer cause and effect relationship
Describe case control study, including strengths and limitations.
Examines exposure and outcome in a group that has the outcome of interest, e.g., cancer, compared to a group that do not have the outcome.
Strength:
- useful in establishing the aetiology of rare diseases
- useful in studying diseases with a long latent period
- allows multiple risk factors to be investigates
- no follow up required
Limitations:
- not useful when establishing rare causes of disease
- prone to multiple bias
- unable to infer cause/effect relationship
Describe cohort study, including strengths and limitations, and an example of a cohort study.
Cohort studies follow a group of people (the cohort) over a long period of time, with consistent monitoring to investigate the relationship between exposure and outcomes within a population.
Can be retrospective or prospective.
E.g., The EPIC (European prospective investigation into cancer) Norfolk study.
Strengths:
- useful when investigating rare exposures
- can infer a cause and effect relationship
- allows the study of multiple exposures on different outcomes
Limitations:
- not useful when investigating rare diseases
- time consuming and expensive
- labour intensive
- high drop out rate
Describe experimental study, including its strengths and weaknesses.
Experimental study is designed to test whether a group of people deliberately exposed to a variable have a different outcome to a group not exposed to a variable.
Experimental study can be carried out at individual or population level.
In randomised control trials (RCT) people are randomly assigned to either the case or control group. The case group are exposed to a variable, the control group are given a placebo. Differences in outcomes between the two groups are measured and considered attributed to the intervention.
Strengths:
- gold standard of determining cause/effect relationship between two variables
- little chance of bias
- little chance of confounding variables
Limitations:
- ethical limitations
- results may not be applicable to real life setting
- time consuming and expensive
Describe relative risk, including how you would calculate relative risk and how results are interpreted.
Relative risk (RR) compares the risk of a health event in one group, compared to the risk of that health event in another group.
RR =
risk of disease in group of primary interest (exposed group) / risk of disease in comparison group (non-exposed group)
risk of disease in exp. group = no. of cases of disease / total in exp. group
risk of disease in non exp. group = no. disease cases / total in non exp. group
RR 1.0 = equal risk between the two groups
RR > 1.0 = exposure increases risk of disease
RR < 1.0 = exposure may be protective against disease
If the RR is 5.34, you subtract 1.0 (as this is equal risk) so the result would be:
exposure increases risk by 434%.
Describe odds ratio, including how you would calculate OR and how results are interpreted.
Odds ratio represents the odds that an exposure will result in an outcome, compared to the odds of the outcome occurring without the exposure.
Case group (exposed) and control group (unexposed) are divided into disease and no disease group.
OR = exposed with disease (A) x unexposed no disease (D) / (exposed no disease (B) x unexposed no disease (C).
A x D / B x C = OR
OR 1.0 = odds of outcome are equal for the exposed and unexposed group
OR > 1.0 = increased risk of the outcome in the exposed group
OR < 1.0 = decreased risk of outcome in the unexposed group (exposure could be a protective factor).
