Analytical Studies

Question 1

What type of design as a case control study?

Answer 1

Retrospective

Question 2

Why is case control study retrospective?

Answer 2

Both exposure and disease have occurred before onset of study

Question 3

Which study is often used first to study a suspected association of causality?

Answer 3

Case control

Question 4

When is a case control study most useful?

Answer 4

In diseases where exposure is common but disease only occurs in small proportion of those exposed

Question 5

Advantages of case control study

Answer 5

Easy to carry out
Less time consuming
Less expensive
Suitable for investigating rare diseases
Subjects not exposed to new risks
Several etiological factors for single disease can be studies
No attrition problems

Question 6

Disadvantages of case control studies

Answer 6

Prone to selection and recall bias
Control group selection may be difficult
Incidence cannot be measured
Cannot prove causality
Temporality is difficult to determine retrospectively
Defining a case is crucial - strict diagnostic criteria & eligibility criteria needed

Question 7

What cannot be calculated in case control studies?

Answer 7

Incidence

Relative risk

Question 8

Where can cases in case control studies be obtained from?

Answer 8

Hospital or general population

Question 9

What must controls by definition in case control studies be?

Answer 9

Identical to cases except for presence or absence of disease and recruited independently of exposure status

Question 10

What can controls be in case control studies?

Answer 10

Hospital patients with different health problem to that studied
Relatives of patients studied
Neighbourhood controls
General population controls

Question 11

Up to what ratio does the pwer of study increase as number of control increases?

Answer 11

4:1

Question 12

What is done to ensure comparability of cases to controls in case control studies?

Answer 12

Matched e.g. by age, sex

Question 13

How can matching occur in case control studies?

Answer 13

Groupwise

Pairwise - more time consuming

Question 14

What can overzealous matching of controls in case controls lead to?

Answer 14

Difficulty in recruiting controls
Reduce risk difference between two groups
May inadvertently result in matching for putative causal factors

Question 15

What is used to estimate risk of exposure to case control studies?

Answer 15

Cross-product ratio called odds ratio

Question 16

Why can incidence rates not be calculated in case control studies?

Answer 16

No longitudinal observation see new cases developing

Question 17

At what point will odds ratio approximate the relative risk in case control studies?

Answer 17

If disease is very rare - <5%

Question 18

Values of odds ratio

Answer 18

0 to infinity i.e. no negative values

Question 19

Implication of there being no negative value for odds ratio?

Answer 19

Log transformations needed to calculate confidence intervals

Question 20

Describe a cohort study

Answer 20

Group of people sharing common aspect

Question 21

What is exposure cohort?

Answer 21

Group of people exposed to a risk factor

Question 22

What is an inception cohort?

Answer 22

Group of patients assembled at a single point of time based on a common factor

Question 23

What happens in cohort studies?

Answer 23

Exposure cohorts are followed up in parallel in non-exposed group to detect development of disease

Question 24

When is cohort studies useful?

Answer 24

When exposure is rare but likelihood of disease is notably high after exposure

Question 25

When are cohort studies only possible?

Answer 25

Easily obtainable, cooperative and stable cohort that can be followed up is available

Question 26

Criteria for non-exposed control in cohort studies

Answer 26

Comparable to study cohort in all respects except for exposure
Must not have disease at time of inception of study

Question 27

How can control group in cohort studies be divided?

Answer 27

Internal control

Exetrnal control

Question 28

What is internal control in cohort studies?

Answer 28

Sbbgroups in exposure cohort according to dose/degree of exposure

Question 29

How can relative risk be calculated in cohort studies?

Answer 29

Ratio of disease (outcome) in exposed group to disease in non-exposed group

Question 30

Determination time in cross-sectional studies

Answer 30

Current estimate of exposure and outcome

Question 31

How are subjects in case-control identified?

Answer 31

According to disease (outcome) status

Question 32

How are subjects in prospective studies identified?

Answer 32

Exposure status

Question 33

How are subjects in retrospective studies identified?

Answer 33

Exposure status

Question 34

Determination time in prospective studies

Answer 34

Current estimate of exposure to future estimate of outcome

Question 35

Determination time in retrospective stdies

Answer 35

Past estimate of exposure to current or past estimate of outcome

Question 36

Advantages of cohort studies

Answer 36

Less prone to selection and recall bias
Incidence & relative risk can be measured
Causal associations can be strongly supported
Temporality easily established
Multiple effects of single exposure can be observed
Dose-response relationships can be calculated
Natural course of exposure to disease pathway can be studied

Question 37

Disadvantages of cohort studies

Answer 37

Time & resource consuming
Not suitable for investigating rare diseases
Only one aetiological factor can be studied at a time
Attrition rate is an issue

Question 38

What is a nested case-control study?

Answer 38

In which both cases and controls are drawn from within a cohort rather than including entire cohort population in a study

Question 39

Advantages of nested case-control studies?

Answer 39

Cheaper and can produce same findings with almost same level of precision