Epidemiology

Question 1

What is epidemiology?

Answer 1

Medical science that studies disease frequences to make inferences about aetiology, prognosis and therapeutic interventions

Note: only makes inferences, never causal relations

Question 2

What does aetiologic research focus on?

Answer 2

Association between risk factors and disease (so: (possible) cause of disease)

Question 3

What does prognostic research focus on?

Answer 3

Predicting the progression or outcomes of disease

Question 4

What does therapeutic epidemiology focus on?

Answer 4

Effects of new treatments, drugs or vaccines

Question 5

What is prevalence? How is it calculated?

Answer 5

Proportion of the population with the disease at a specific point in time
Diseased/total population or D/N

Question 6

What is incidence? Which two types are there?

Answer 6

Proprotion of the populatin at risk newly developing disease in a specific period of time
Two types:
-Cumulative incidence (CI)
-Incidence rate (IR)

Question 7

How is cumulative incidence calculated?

Answer 7

Diseased/population at risk
Note: always over a specific period of time

Question 8

How is incidence rate calculated?

Answer 8

Diseased/person-years at risk
Note: always over a specific period of time

Question 9

When is cumulative incidence used, and when is incidence rate used?

Answer 9

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)

Question 10

What is the systemic collection of descriptive information of diseases called?

Answer 10

Surveillance

Question 11

Why is randomization employed?

Answer 11

(Good) randomization leads to a similar population in the control group vs. the active group -> both are representative of the total population

Question 12

What is the only study type that can provide definite proof of the efficacy of new treatments/drugs/vaccines?

Answer 12

Randomized controlled trial

Question 13

What is a cohort study?

Answer 13

A study that studies a cohort = group of people with the same condition/exposure

Question 14

What is the difference between a ‘normal’ cohort study and an RCT?

Answer 14

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)

Question 15

What kind of measures do cohort studies provide?

Answer 15

Measures of association -> incidence rate ratio (IRR), relative risk (RR), hazard ratio (HR), odds ratio (OR)

Question 16

What is an intention-to-treat analysis? What is its advantage?

Answer 16

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

Question 17

What is required for a study to have high external validity? Why is this a problem with RCT’s?

Answer 17

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.

Question 18

What is a case control study? What information does it provide?

Answer 18

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

Question 19

What is the advantage of retrospective cohorts studies and case control studies?

Answer 19

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

Question 20

Why is the validity of a case control study or retrospective cohort study lower than that of a prospective cohort study or RCT?

Answer 20

Because the study population cannot be selected and/or controlled

Question 21

What is a null hypothesis (H0)?

Answer 21

The hypothesis that a certain intervention has no effect

Question 22

What is an alternative hypothesis (HA)?

Answer 22

The hypothesis that a certain intervention does have an effect

Question 23

What is a type I error?

Answer 23

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

Question 24

What is the usual threshold/critical value for the type I error?

Answer 24

95% confidence or p < 0.05

Question 25

What does a Chi-square test do?

Answer 25

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)

Question 26

What is the disadvantage of a p-value vs. a 95%CI?

Answer 26

The 95%CI shows an effect size, the p-value does not and only indicates whether there was a significant assocation

Question 27

The larger the sample size, the [easier/harder] it is to find statistically significant results

Answer 27

Easier

Question 28

The larger the sample size, the [narrower/wider] the 95%CI

Answer 28

Narrower