Epidemiological Study Design 1

Question 1

What is a cross sectional study

Answer 1

type of observational study that analyses data from a population, or a representative subset, at a specific point in time

Question 2

Strengths of a cross sectional study

Answer 2

quick

relatively cheap and simple

Question 3

Weaknesses of a cross sectional study

Answer 3

not useful for rare exposures or diseases

cannot assess causation as don’t know whether outcome or exposure came first

Question 4

What are cohort studies?

Answer 4

define groups on exposure
type of longitudinal study
perform cross-sections at intervals of time, looking for outcome

Question 5

Strengths of cohort studies

Answer 5

know of exposure before disease (outcome), therefore measurement of exposure not likely to be biased by disease
look at multiple outcomes easily
direct assessment of incidence
good for rare exposures

Question 6

Weaknesses of cohort studies

Answer 6

poor design for rare outcomes
slow and expensive, have to wait for outcomes
attrition
selection bias if exposed and unexposed not representative

Question 7

Retrospective cohort studies

Answer 7

cohort study using data gathered in the past for exposure and outcome
allows cohort studies to be conducted more quickly and cheaply

Question 8

What are case control studies?

Answer 8

observational study in which two existing groups differing in outcome are identified and compared on the basis of some supposed causal attribute

Question 9

Strengths of case control studies

Answer 9

efficient for rare outcomes/diseases with long latency between exposure and disease
cheap and quick
easy to study multiple exposures
good for populations where follow up is difficult

Question 10

Weaknessed of case control studies

Answer 10

prone to bias
can study only one outcome
poor for studying rare exposures
cannot usually allow direct calculation of incidence rates

Question 11

Ecological studies

Answer 11

observational study where data is analysed at the population or group level, rather than individual level
often used to measure prevalence and incidence of disease, particularly when disease is rare

Question 12

Strengths of ecological studies

Answer 12

quick and cheap

generate hypotheses to examine at individual level

Question 13

Weaknesses of ecological studies

Answer 13

different areas may not have same ascertaianment or recording of disease
differences in measurement of exposure
relationships found at population level may not hold true at an individual level