Week 3

Question 1

descriptive cross sectional study

Answer 1

describe frequency of exposure or outcome in a defined population

Question 2

analytical cross sectional study

Answer 2

collects information on both the outcome of interest and potential risk factors in a defined population
then compare the prevalence of the outcome in the people exposed to each risk factor with the prevalence in those not exposed

Question 3

what does a cross sectional study do

Answer 3

estimate frequency or outcome at a particular point in time

Question 4

why do a cross-sectional study

Answer 4

health service planning- prevalence of specific outcome in a defined population at point in time
useful for assessing burden of disease and planning preventative and curative services

Question 5

main steps of a cross sectional study

Answer 5

1. defining the study
2. defining the target population
3. selecting the study population
4. collecting data
5. analysing data
6. interpreting results

Question 6

survey sampling

Answer 6

can make statements about the population by asking a small sample

Question 7

convenience samples

Answer 7

ie patients attending a clinic
is the group representative

Question 8

random sample

Answer 8

each subject has equal chance
computer generate random numbers

Question 9

stratified sampling

Answer 9

population divided into groups (based on similarities)
take random sample from each group

Question 10

pitfalls in surveys

Answer 10

inaccurate data
non-coverage
non-response

Question 11

analysis of cross sectional studies

Answer 11

prevalence ratio: prevalence of outcome in exposed

Question 12

interpretations of cross sectional studies

Answer 12

true association or reverse causality
random error
bias
confounding

Question 13

bias in cross sectional studies

Answer 13

selection bias: characteristics of those taking part vs those not taking part
information bias: recall bias

Question 14

how to minimise bias in cross sectional studies

Answer 14

by having strict case definition for the outcome of interest
using standardised methods of data collection
ensuring that the researcher who assigns the diagnosis is blinded to exposure status

Question 15

strengths of cross-sectional study

Answer 15

easy and economical
provides important information on the distribution and burden of exposures and outcomes- valuable for health-service planning
can be used as the first step in the study of a possible exposure-outcome relationship

Question 16

weakness of cross-sectional studies

Answer 16

measures prevalent rather than incident cases
can be difficult to establish the time-sequence of events in a cross-sectional study
- the exposure may have occurred as a result of the outcome (reverse causality)

Question 17

definition of ecological studies

Answer 17

observational study with populations or groups (instead of individuals) being unit of observation

Question 18

what does ecological studies do

Answer 18

compare group averages
- health
- risk factors

Question 19

interpretations of ecological studies

Answer 19

true casual (association) or reverse causality
random error
bias
confounding

Question 20

uses of ecological studies

Answer 20

describes associations at group level
quick and cheap- routine data
generates hypotheses- first step
some risk factors may not easily be measurable at an individual level

Question 21

what is ecological fallacy

Answer 21

ecological studies enable us to make ecological inferences about effects at the group level. They do NOT enable us to make inferences about individual risks
an attempt to infer from the ecological level to the individual level is often called ecologcil fallacy