Epidemiology Flashcards
What is epidemiology?
Medical science that studies disease frequences to make inferences about aetiology, prognosis and therapeutic interventions
Note: only makes inferences, never causal relations
What does aetiologic research focus on?
Association between risk factors and disease (so: (possible) cause of disease)
What does prognostic research focus on?
Predicting the progression or outcomes of disease
What does therapeutic epidemiology focus on?
Effects of new treatments, drugs or vaccines
What is prevalence? How is it calculated?
Proportion of the population with the disease at a specific point in time
Diseased/total population or D/N
What is incidence? Which two types are there?
Proprotion of the populatin at risk newly developing disease in a specific period of time
Two types:
-Cumulative incidence (CI)
-Incidence rate (IR)
How is cumulative incidence calculated?
Diseased/population at risk
Note: always over a specific period of time
How is incidence rate calculated?
Diseased/person-years at risk
Note: always over a specific period of time
When is cumulative incidence used, and when is incidence rate used?
Cumulative incidence is used in closed populations (does not account for drop-outs and does not allow for influx of new people in the population at risk)
Incidence rate is used in dynamic populations (allows to account for people coming into the population or leaving the population throughout the observation period)
What is the systemic collection of descriptive information of diseases called?
Surveillance
Why is randomization employed?
(Good) randomization leads to a similar population in the control group vs. the active group -> both are representative of the total population
What is the only study type that can provide definite proof of the efficacy of new treatments/drugs/vaccines?
Randomized controlled trial
What is a cohort study?
A study that studies a cohort = group of people with the same condition/exposure
What is the difference between a ‘normal’ cohort study and an RCT?
A cohort study follows a cohort of patients over a period of time to track the development of an outcome of interest
A RCT tests the specific effect of an intervention (note: RCT is a type of cohort study)
What kind of measures do cohort studies provide?
Measures of association -> incidence rate ratio (IRR), relative risk (RR), hazard ratio (HR), odds ratio (OR)
What is an intention-to-treat analysis? What is its advantage?
Analysis of the results of all participants starting a trial, irrespective of whether they adhere to treatment
This accoutns for people stopping the drug because of side effects/other reasons and doctors stopping drugs -> mimics a real life situation and thus more accurately displays drug performance in real-life situtation
What is required for a study to have high external validity? Why is this a problem with RCT’s?
The need to be reproducible; this is hard for RCT’s because differing standards of care, populations, etc.
If I try to repeat a study from the US in Indonesia, I have a different standard of hospital care, different patient population, etc.
What is a case control study? What information does it provide?
Compares exposure frequencies in cases with a particular condition vs. controls
When I find that people with a disease have significantly more exposure to a risk factor, this provides an association between the risk factor and disease in the form of an odds ratio (OR)
Note: case control studies are always retrospective
What is the advantage of retrospective cohorts studies and case control studies?
They take less time to conduct than a prospective cohort or RCT -> you don’t have to wait for events to occur or to find a trial population
Why is the validity of a case control study or retrospective cohort study lower than that of a prospective cohort study or RCT?
Because the study population cannot be selected and/or controlled
What is a null hypothesis (H0)?
The hypothesis that a certain intervention has no effect
What is an alternative hypothesis (HA)?
The hypothesis that a certain intervention does have an effect
What is a type I error?
Rejection of the null hypothesis when it is actually true for your population
In other words: inferring there is an effect of an intervention, when there is actually no effect
What is the usual threshold/critical value for the type I error?
95% confidence or p < 0.05
What does a Chi-square test do?
Compares the observed values in the study with the values that would be expected if the null hypothesis is true (=if there is no effect)
When the alternative hypothesis is more likely than the null hypothesis by a margin of 95%, the alternative hypothesis is adopted (significant result)
What is the disadvantage of a p-value vs. a 95%CI?
The 95%CI shows an effect size, the p-value does not and only indicates whether there was a significant assocation
The larger the sample size, the [easier/harder] it is to find statistically significant results
Easier
The larger the sample size, the [narrower/wider] the 95%CI
Narrower
