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Summary - Essential epidemiology: an introduction for students and health professionals
1 Epidemiology is...
What is epidemiology?
It is about measuring helath, identifying the causes of ill-health and intervening to improve health. It is about who, where, when, why, and what
How to calculate the relative risk?
Attack Rate (%) who ate the food/ Attack Rate (%) who didn't eat the food
The risk of people who didn't eat the food, relative to the ris of people who ate the food.
What epidemiologists do;
-Descriptive studies by person, place and time
1.1 Study designs
Frequency/amount of disease or other characteristics in a population (person/time/place)
Typical study designs; survey and cross sectional study
What, Who, When, Where
Study of the causes of a disease, exposure- disease associations
Typical study designs;
* observational; ecological, cross sectional, cohort, case control study
* experimental; randomized controlled trial
Describe groups of people (demographics, risk factors, disease status), important to have a representative group
Cross- sectional study
All variables (exposure and outcome) are measured at the same moment in time. You take a snapshot of the situation
'' is this related to that? and/or to that?''
Disadvantage; you don't know the cause for sure (reverse causation, confounding)
-> Ask 1000 people about their current mobile phone use, and whether they suffer from headaches. Check whether the two are linked.
Outcome can influence the exposure, association in wrong direction
prospective, longtitudanal, forward in time.
1. Exposed; disease/ no disease
2. Not exposed; disease/ no disease
The most computed measures are the incidence rate (by person years) and the incidence proportion, and the attack rate (eigenlijk attack proportion!!!)
Case control study;
backward in time/ retrospective. Exposure in past comparing.
1. study participants
2. outcome present?
2a. no; risk factor present?
2a. yes; risk factor present?
In case of a case-control study you measure neither prevalence or incidence because you determine the amount of people which is artificial. Prevalence/ Incidence only if you know total amount of people.
An observational study in which the unit of analysis is a population or a group instead of an individual
Fallacies of ecological studies;
- not so good to determine cause
- Assumption that individual members of a group have the average characteristics of the group at large.
However; Statistics that accurately describe group characteristics do not necessarily apply to individuals within that group.
Common in ecological studies;
- inverse association; negative association; the more.... the lower....
- positive association; the more.... the more..... (healthy or unhealthy)
can give insight in genetic vs. environmental influences. No control group. '' Natural experiment''
Main difference between observational and experimental is that the investigator assigns the exposure (randomly) in a trial
Defined population --> randomising to groups; 1. exposed (diseas/no disease) 2. not exposed (disease/ no disease)
Strongest prove for causality; highest intern validity because you get rid of confounding because of random assignment
The observed association between exposure and outcome is caused by a third variable that is not part of the biological pathway
Hierarchy of epidemiologic study designs; from generate hypotheses till establish causality;
1. case reports
2. case series
3. ecologic studies
4. cross sectional studies
5. case control studies
6. cohort studies
7. randomized controlled trials
Doctors description and interpetation of individual patients.