Introduction/ Measures and Frequency of Association. Flashcards
What does a disease determinant result in?
A change in disease status between populations.
Who is widely considered the fist epidemiologist?
Hippocrates (460-370bc).
If a disease is present at stable frequencies what can it be described as?
An endemic.
Acute events rarely occur with a chronic condition. True or False?
False, they can occur.
John Gaunt is widely known for being the first person to systematically collect data, including birth and death rates of populations. What did this collection quantify the death rate of children to be?
What are two other examples of data that were collected?
1/3 dead by the age 5.
This is still the case in developing countries.
- Plague deaths.
- Incidence rate of rickets.
What is a time series?
The distribution and prevalence of something in a population over a period of time.
In the mid 70’s alcohol was linked to colorectal cancer. What chemical compound was responsible for this link and where was this compound specifically found?
Nitrosamine, found in dark beer.
One the link between alcohol and colorectal cancer was made what intervention(s) was made to prevent this link from occurring in the future?
- Gas ovens used to produce beer were replaced by electric (gas was reacting with natural amines producing the nitrosamine).
- Beer was tested from the 1980’s for nitrosamine.
Which is more descriptive/analytical, classical or modern epidemiology?
Classical.
Which is more experimental, classical or modern epidemiology?
Classical.
Which is focused on risk factors opposed to causes, classical or modern epidemiology?
Modern.
Which is focused more on chronic disease, classical or modern epidemiology?
Modern (but classical is also).
What does causal inference aim to do?
Identify determinants of disease and eliminate the casual effects of the exposure of a disease.
Name 3 frequency measures.
Proportion, rate, odds.
Do the two quantities used to calculate a ratio need to be related?
No.
What is the prerequisite for something to be a proportion?
N needs to be in D.
What does the denominator need to be for the measurement need to a rate?
A measure of person time.
What type of prevalence takes into account the entire period of interest?
Period.
What is point prevalence often expressed as?
A percentage.
What needs to be stated when stating a point prevalence?
A given time point.
Why would the prevalence of the common cold be calculated as a point prevalence rather than a period prevalence?
The time course is too short.
What can you not infer from prevalence?
Causation.
What two things does prevalence reflect?
The incidence rate (IR) and the duration of the disease (D).
Name three scenarios that will decrease the prevalence of a disease?
- Occurrence decreases.
- Cases are cured.
- Cases die earlier.
What is cumulative incidence defined as?
Proportion of a population with a new event during a given time period.
What does cumulative incidence measure?
Occurrence of a disease within a population.
Why does cumulative incidence need a timepoint?
As it is cumulative? Ie it will eventually reach 1.
What is the equation for cumulative incidence?
Number of new cases during a given time period/ Number of disease free individuals at the start of the time period.
What is cumulative incidence also known as?
Incidence proportion/ risk.
What is the definition of ‘Attack Rate’.
Proportion of individuals that develop an infectious disease during an outbreak. (Not a true rate).
What is the definition of ‘Case Fatality Rate’.
Proportion of cases who die among those who develop the disease. (Not a true rate).
cumulative incidence cannot be estimated from cross sectional studies or surveys. What can?
Prevalence.
What is the survival proportion equal to?
1 - cumulative incidence.
What is the definition of a competing risk?
An event that removes a subject from being at risk from the outcome of interest.
What is the definition of person time?
The sum of the individual time period spent in the cohort by each individual.
Is person time a rate?
Yes.
What is the definition of incidence rate?
Number of new cases during follow up/ total person time contributed by disease free individuals.
How can you minimise competing risk (2 ways)?
- Look at incidence rate/ person time instead of just CI.
2. Reduce the time of follow up.
How can you work out the average density of cumulative incidence during a short time period?
C/ NΔT. = CI/ΔT.
What does NΔT equal?
Approximate person time during Δt ( a short time interval).
Why is the actual person time slightly less than NΔT ?
As some people will develop the disease in this periodn of time despite the short time period.
What is the equation for working out odds/ proportion?
Odds = Proportion/ 1- proportion.
Why is there more discrepancy between odds and proportions when both get larger?
As proportions can not exceed 1.
Presuming that CI (IR) and D are constant over time and that the population is in steady state what can prevalence be defined as?
Prevalence = IR x D.
CI can be calculated from the incidence rate by what equation?
CI= 1-e^(-IR x t).
What two scales can quantify the strength of an association?
- Multiplicative.
2. Additive.
What is the definition of a counterfactual?
Potential outcomes that would have been observed under each possible exposure/ treatment value. For some subjects these are outcomes that they would not have experienced.
What would need to happen for a causal relationship to actually be determined?
Each individual would need to experience both counterfactuals. This can’t happen.
What does ‘the endpoint of a casual mechanism’ define?
An effect.
In terms of the Bradford Hill criteria does a small association mean no effect?
No.
What does the Temporality part of the Bradford Hill Criteria state?
Effect must be after cause with the expected time delay.
What does the Biological gradient part of the Bradford Hill Criteria state?
Greater exposure should lead to greater incidence. In some cases the presence of a specific factor can trigger an effect.
Absolute effects are differences in incidence rates, cumulative incidences and prevalence. All of these have an additive scale. What sort of effects are relatives of these measures and have a multiplicative effect?
Ratios.
What sort of measure is a risk difference?
An absolute measure.
What is the equation for risk difference?
CID = CI1- CI2.
What is the equation for risk ratio?
RR= CI1/CI2.
What sort of effect does a odds ratio show?
An individual effect.
