SEM 2

Question 1

What questions do descriptive studies involve?

Answer 1

How does the risk of developing the disease vary over time?
How does it vary from place to place?
How does it vary with age, sex, occupational group?

Question 2

What questions do analytic studies involve?

Answer 2

Do people w characteristic have the disease more frequently than those who don’t? (Cross-sectional studies)
Do people w characteristic develop disease more frequently than those who don’t? (Longitudinal / Cohort studies)
Do persons w disease have characteristic more frequently than those w/o disease? (Case-control studies)

Question 3

What question do experimental studies involve?

Answer 3

Does altering / removing characteristic reduce probability of developing disease?

Question 4

What’s ecological studies?

Answer 4

Analytical, describes outcome in populations + exposure
Average exposure of a population vs rate of outcome for that population
Evidence of an association examined using correlation or regression
Can’t comment on individual exposure + risk of outcome – “ecological fallacy”

Question 5

Define ecological fallacy

Answer 5

Can’t comment on individual exposure + risk of outcome

Question 6

What are the advantages of ecological studies?

Answer 6

Cheap + quick
Routine data available
Exposure info available at area level
Area diff in exposure larger than individual diff in one area
Generates hypotheses

Question 7

What are the disadvantages of ecological studies?

Answer 7

Proxy measure of exposure as based on average for a population
Area diff in recording or disease
Systematic diff in exposure measure
Data on confounders unavailable
Boundaries may inappropriately divide

Question 8

Key message of descriptive/ecological studies?

Answer 8

good for describing magnitude of disease burden, but limited when we want to identify causes

Question 9

What’s prevalance?

Answer 9

number of cases (outcomes) present at point in time per recruited (defined) study population i.e.proportion w outcome of interest
E.g. 5 per 100,000
3 per 100 = 3%

Question 10

What question do cross-sectional studies answer?

Answer 10

Are people w characteristic (the exposed) more likely to have disease than those who don’t (non-exposure)?

Question 11

What’s the advantage of analytic studies?

Answer 11

both disease + exposure info obtained on sample of population so:
multiple causes of given disease studied
multiple consequences of given exposure studied

Question 12

What’s cross-sectional studies + diff types?

Answer 12

Measures individual prevalence of exposure or outcome
‘Point prevalence’ or ‘period prevalence’
Descriptive if outcome unreported in relation to exposure or if exposure unreported in relation to outcome
Analytical if disease prevalence compared in those w + w/o exposure

Question 13

What are the advantages of cross-sectional studies?

Answer 13

Simple to conduct
Quick + cheap
Used for planning
Estimate prevalence of common conditions of sufficient duration
Estimates exposure in a population

Question 14

What are the disadvantages of cross-sectional studies?

Answer 14

Can’t answer if outcome followed the exposure or exposure followed outcome
No measure of incidence
Useless for rare disease (or exposure); need large sample size

Question 15

What’s longitudinal/ cohort studies + features?

Answer 15

Measurements of disease and/or exposure taken at 2 or more points in time.
They include:
-descriptive studies of disease incidence, natural history or human growth + development
-analytical studies of relating measures of disease to prior observations on exposure in the same subjects

Question 16

Describe longitudinal/prospective cohort study

Answer 16

observational study where population studied for presence of characteristic (blood group) or exposure (smoking), which is thought to be cause of condition (cancer), prior to the onset. Population followed up over time, incidence in exposed individuals compared to unexposed

Question 17

What’s longitudinal/prospective cohort study based on?

Answer 17

asking

Question 18

What question does longitudinal/prospective cohort study answers?

Answer 18

Do people w characteristic / exposure develop disease more frequently than those w/o characteristic?

Question 19

Define cohort study

Answer 19

group of people EXPOSED + group of people UNEXPOSED to RISK FACTOR are followed-up in time

Question 20

What calculations are made from cohort studies?

Answer 20

Incidence of OUTCOME in one group compared w other. Measures of RELATIVE RISK + ABSOLUTE RISK can be calculated

Question 21

What are the advantages of cohort studies?

Answer 21

Direct measures of incidence + prevalence
Multiple outcomes + exposures
Good for rare exposures
Exposure measured prior to disease

Question 22

What are the disadvantages of cohort studies?

Answer 22

Bias if loss to follow-up
Bias if outcome not assessed similarly in exposed + unexposed
Inefficient for rare disease
Expensive + slow