Summary Study Guide Epidemiology and Global Health per Problem (PBL)

Study Guide Epidemiology and Global Health

Problem 1 – Study Designs
 Study design: plan of how to conduct a study to answer a hypothesis

Observational study (measured by observation, not intervened)
- Descriptive (describe the occurrence of disease)
o Used to make hypotheses
- Analytical (analyses the relationships between exposure and disease)
o Ecological (population)
 Correlational
 Generate hypotheses
 Unit: groups of people
 Advantages: use populations with differing characteristics, and
existing data can be used
 Test for potential confounders
o Cross-sectional (individual)
 Measure of exposure at a given point of time
 Key question: does the exposure precede or follow the effect?
 For fixed exposures (ethnicity, blood type)
 Advantages: the timing of the exposure is known (whether it
happened before or after the exposure), and looking at the
possibility causes of disease can make the study successful
 If exposure is not measured before the disease the study gives
disease prevalence
 Recall bias is high (people might not remember how much they
smoke for example)
 Trends can be measured if people are examined in several
points in time
o Case control
 On people that have the disease
 Backtrack what leads to the disease
 Compared to people without the disease to see normal
occurrence with similar characteristics
 Disadvantage: can be biased as the past is examined, and it is
hard to find control groups that are very similar
 Relative risk is calculated (compared to controls)
o Nested case control studies
 Using cases from cohorts for which exposure information is
already available (checking whether they had the disease or
not)
 Cohort is already designed
o Cohort
 Aka follow-up study
 Start with healthy people (see whether they get the disease
during the follow-up)
 Can be pro and retrospective study
 (Difference from case control is that the subjects are healthy to
start out with)
 Advantages: insight into pattern of exposure and the disease,
and insight into causality

,  Disadvantages: expensive, and large group is required

Experimental study (assign exposures, manipulate certain factors and measure the
effect)
- Randomized control trial
o Randomly selected people from two groups and are compared
o E.g. vaccine studies
- Field trial
o On healthy, but presumed to be at risk
o Data collection takes place in the field
o E.g. lead levels in children for those that were raised under lead
regulated environments compared to those that were not
- Community trials
o Do not focus on the individual
o Good to measure disease that affect the community (eg
cardiovascular disease)
o See the effects of social conditions on disease development




Sources of error:
- Random error (eg variation in people and by chance in small sample)
- Systematic error
o Selection bias
o Measurement error
 Recall bias
 Observer bias
o Response bias
- Confounding