Exam questions Flashcards
Definitions and exam-style questions
define prevalence
the number of affected persons present in the population divided by the number of people in the population.
explain the relationship between prevalence and incidence.
Prevalence is the number of existing cases within a population, whereas incidence is the number of new cases within a population.
define stillbirth rate
The number of stillbirths for every thousand live births in a country.
define life expectancy
the number of years a baby born today can be expected to live if it experienced the current age-specific mortality rates.
define healthy life expectancy
the number of expected years of life in good or fairly good general health.
define infant mortality rate
the number of dead infants (from age 0-1 years) that year against the number of live births that year.
define the PYLL index
potential years of life lost
the number of years of life lost when a person dies prematurely.
a measure of the relative impact of various diseases and lethal forces on society.
define the total period fertility rate
the average number of children that would be born to a woman over her lifetime.
what are the key design features of a cross-sectional study?
- Defining the study question
- Defining the target population
- Selecting the study population
- Collecting data
- Analysing data
- Interpreting results
what are the two main sources of bias in a cross-sectional study?
selection bias
information bias - recall bias
what are the key design features of a randomised controlled clinical trial?
PICO:
population
intervention
comparator
outcome
What are the two main sources of bias in a randomised controlled clinical trial? Give an example of each.
Performance bias
what are the key design features of a case-control study?
- decide sample size
- case selection
- control selection
- collect exposure data
- data analysis
- deal with validity threats
What are two of the main sources of bias in a case-control study? Give an example of each.
selection bias
information bias
What is matching in a case-control study and why is it used?
when variables between people are matched based on similar traits they have, to reduce the effect of confounding variables
write short notes on relative risk
Relative risk is the probability of an event occuring in the treatment group compared to the control group.
It can be calculated by
write short notes on population attributable risk
the proportion of the disease in the population that could be eliminated if exposure were eliminated.
expressed as a percentage of total risk in the population.
helps determining exposures relevant to public health in community.
reduction in risk is achieved if the population is entirely un-exposed.
write short notes on NNT
NNT= the number needed to treat
NNT is the number of patients you need to treat to prevent one additional bad outcome (death, stroke, etc.).
For example, if a drug has an NNT of 5, it means you have to treat 5 people with the drug to prevent one additional bad outcome.
write short notes on selection bias
Selection bias is when the initial cohort used in the study is not representative of the rest of the population,
write short notes on information bias
Information bias is when any systematic difference from the truth that arises in the collection, recall, recording and handling of information in a study, including how missing data is dealt with.
example = misclassification bias
what is the evidence pyramid for study designs?
Studies are assigned levels of evidence based on their methodology. The evidence pyramid is an easy way to visualize this hierarchy of evidence.
The top of the pyramid represents the strongest evidence.
At the base of the pyramid is unfiltered evidence including randomized controlled trials, cohort studies and case reports. These are individual reports and studies, also known as the primary literature.
what is the difference between necessary and sufficient cause?
Necessary cause has to be present for the disease to occur, for example, HIV has to be present for AIDS to occur.
A set of conditions is a sufficient cause when it always produces the outcome, for example, heavy smoking and lung cancer.
what is the epidemiological triangle?
the epidemiological triangle is used to determine the cause of infectious disease, non-infectious diseases and accidents or injuries.
It is made up of 3 parts:
- Host (intrinsic factors)
- Agent
-Environment (extrinsic factors)
Example when it is used - Tuberculosis
Host = poor nutrition, recurrent disease, low immunity
Agent = TB organism
Environment = crowding, poor ventilation, bad sanitation
what are Bradford Hill’s criteria of causation?
- strength of association
- consistency - replication
- specificity of the association
- temporal sequence
- biological gradient
- coherence
- experiment
- theoretical plausibility
- analogy
What does temporality mean?
the effect has to occur after the cause, and if there is an expected delay between the cause and expected effect, then the effect must occur after the delay.
In some circumstances it is not feasible to carry out individually randomised trials: name 2 alternative designs.
parallel studies
cross-over studies
Select one alternative to randomised control trials and outline the main design features of it.
parallel studies
What is an SMR and when is it used in epidemiology?
standardised mortality ratio
a measure used to quantify an increase or decrease in mortality in a study cohort compared to the general population
calculated from expected deaths in a study population.
What are direct and indirect standardisation?
direct standardisation = when the age specific death rates from a population of interest are taken and applied to the standard population. the new death rate is then calculated from this.
indirect standardisation = when the number of deaths expected is found if both populations had the same age specific death rates, but kept their real age structure.
When is the indirect method of standardisation preferred to the direct?
in small, sub-populations with few cases
what is effect modification? Use an example to illustrate your explanation.
Effect modification = when the effect of a factor is different for different groups.
Example= age, gender, genetics, nutrition
what is a 95% confidence interval?
The 95% confidence interval is a range of values that you can be 95% confident contains the true mean of the population.
what is point prevalence
the proportion of persons in a defined population that has the outcome under study at a specific point in time.
what is period prevalence?
the proportion of persons in a defined population that has the outcome under study over a period of time.
what is prevalence useful for?
Assessing the burden of disease within a population.
Valuable for planning
what is prevalence not useful for?
Determining what caused disease
what are the 2 measures of incidence?
risk
rate
what is incidence risk?
the number of new cases in interval/population initially at risk (e.g. mortality rates)
good for static populations
what is incidence rate?
the number of new cases/total person-time at risk
good for dynamic populations
what is annual incidence?
- count deaths over a calendar year
what is cumulative incidence?
frequency of new cases over a specified period
what is annual incidence useful for?
monitoring trends
sensitive to changes in disease risk
LESS SUITABLE for assessing burden of disease.
what is demography?
the scientific study of human populations
what are crude and age standardised mortality rates?
crude mortality mortality rate = the number of deaths divided by the population of a country
depends on the age/sex of a population
age standardised mortality rate = often used to account for confounding effects of age so that rates of disease or mortality can be compared in populations with different age structures.
how can the confounding variable be controlled for?
- stratification
- matching cases and controls
- multivariable methods
what is effect modification?
a factor which modifies the effect of exposure to a risk factor.
behaves like a confounder but shouldn’t be treated like a nuisance
can be made visible by stratifying by effect modifier
name some factors that are sometimes effect modifiers
- genetics
- age
- gender
- physical fitness
- nutrition
- disease
what is Rothman’s model of causation?
explains that:
- there is no single cause of disease
- the cause of a disease is a constellation of components that act together
what are the two different causes of disease?
- necessary cause
- sufficient cause
what is a necessary cause?
an exposure which is necessary for disease to occur
the exposure must always precede the disease
example= HIV must always be present to cause AIDS
what is a sufficient cause?
a set of conditions is a sufficient cause when it always produces the outcome
example = heavy smoking and lung cancer
what are some sources of routine data?
death certificates
GP records
birth certificates
census, government registers
disease register
educational records
describe a spike population pyramid
high birth rates
high death rates
low growth rate
describe a wedge population pyramid
high birth rate
low death rate
high growth rate
describe a beehive population pyramid
low birth rate
low death rate
low growth rate
