Analytical Studies Flashcards
What type of design as a case control study?
Retrospective
Why is case control study retrospective?
Both exposure and disease have occurred before onset of study
Which study is often used first to study a suspected association of causality?
Case control
When is a case control study most useful?
In diseases where exposure is common but disease only occurs in small proportion of those exposed
Advantages of case control study
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
Disadvantages of case control studies
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
What cannot be calculated in case control studies?
Incidence
Relative risk
Where can cases in case control studies be obtained from?
Hospital or general population
What must controls by definition in case control studies be?
Identical to cases except for presence or absence of disease and recruited independently of exposure status
What can controls be in case control studies?
Hospital patients with different health problem to that studied
Relatives of patients studied
Neighbourhood controls
General population controls
Up to what ratio does the pwer of study increase as number of control increases?
4:1
What is done to ensure comparability of cases to controls in case control studies?
Matched e.g. by age, sex
How can matching occur in case control studies?
Groupwise
Pairwise - more time consuming
What can overzealous matching of controls in case controls lead to?
Difficulty in recruiting controls
Reduce risk difference between two groups
May inadvertently result in matching for putative causal factors
What is used to estimate risk of exposure to case control studies?
Cross-product ratio called odds ratio