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Introduction to Case-crossover
design
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Isfahan- CSC: Clinical Studies CenterBy: Tohid Jafari
Brief introduction to case-crossover design
unusual just before
The simple part of the questionThe challenging part
We need controls to determine what unusual meant. However, using different individuals for comparison is not rationale since everyone is different and has different response to the same exposure.
Brief introduction to case-crossover design
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Isfahan- CSC: Clinical Studies CenterBy: Tohid Jafari
Feel the design…
Feel the design…
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Time is passing
I am so sick…Why??
Did I do something unusual right before
the illness?????
In comparison to my usual???
Have you experienced?Of course you have.
Isfahan- CSC: Clinical Studies CenterBy: Tohid Jafari
Why call it Case-Crossover?
each case is its own controlviewed retrospectively
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Isfahan- CSC: Clinical Studies CenterBy: Tohid Jafari
Starting example
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Isfahan- CSC: Clinical Studies CenterBy: Tohid Jafari
Starting example
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Exposure to a hazard
Higher or lower hazard exposures triggers the event? Depends on the relationship.
Case-control design needs different control in the same time
Case crossover needs the same control at different time
Car with accident
Car without accident
Time
Isfahan- CSC: Clinical Studies CenterBy: Tohid Jafari
the control is the same person at a different time rather than a different person at the same time.
Starting example
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Isfahan- CSC: Clinical Studies CenterBy: Tohid Jafari
Matched pair case-control 2*2:
Q: are exposures are differentin cases and controls?
Case-crossover 2*2:
Q: are exposures are differentin hazard and control periods?
Starting example
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Control period
Expo Unexpo
Hazard period
Exposed a b
Unexpo c d
Controls
Expo Unexpo
CasesExposed a b
Unexpo c d
All subjects are cases.
Isfahan- CSC: Clinical Studies CenterBy: Tohid Jafari
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Despite being similar, previous experience in conducting case-control studies
does not fully prepare you for doing case-crossover study.
Isfahan- CSC: Clinical Studies CenterBy: Tohid Jafari
Terminology used in case-crossover
design
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Isfahan- CSC: Clinical Studies CenterBy: Tohid Jafari
- Case window, or current period, or effect period:
Example
Terminology
✍Exposure A
Effect period
Exposure B Effect period
Isfahan- CSC: Clinical Studies CenterBy: Tohid Jafari
-Hazard period:
Usually the length of hazard period is the same as the length of effect period.
Terminology
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Event onset
Hazard period
Isfahan- CSC: Clinical Studies CenterBy: Tohid Jafari
The length of this period is very important
Terminology
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Isfahan- CSC: Clinical Studies CenterBy: Tohid Jafari
- Control window, or reference period, or control period:
There are 2 types of control data or information:Exposure information from comparable time period
Exposure information according to individual usual exposure frequency
Terminology
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Isfahan- CSC: Clinical Studies CenterBy: Tohid Jafari
Suitable study cases
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Isfahan- CSC: Clinical Studies CenterBy: Tohid Jafari
Study subjects suitable for case-crossover?1- Acute cases2- Crossing over3- Transience of the effect
Study subjects suitable for case crossover?
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Isfahan- CSC: Clinical Studies CenterBy: Tohid Jafari
Pros and Cons
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Isfahan- CSC: Clinical Studies CenterBy: Tohid Jafari
Pros:
Pros and cons
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Isfahan- CSC: Clinical Studies CenterBy: Tohid Jafari
Cons:- Not suitable for chronic diseases:
- Not able to assess long term effects:
- Recall bias:
- Requires careful selection of the length and timing of the windows
Pros and cons
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Isfahan- CSC: Clinical Studies CenterBy: Tohid Jafari
Applications in articles
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Isfahan- CSC: Clinical Studies CenterBy: Tohid Jafari
A case-crossover study of alcohol consumption, meals and the risk of road traffic crashes
Applications in articles
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Isfahan- CSC: Clinical Studies CenterBy: Tohid Jafari
The role of alcohol and drugs in triggering criminal violence: a case-crossover study
Applications in articles
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Isfahan- CSC: Clinical Studies CenterBy: Tohid Jafari
Risk of new acute myocardial infarction hospitalization associated with use of oral andparenteral non-steroidal anti-inflammation drugs
Applications in articles
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Isfahan- CSC: Clinical Studies CenterBy: Tohid Jafari
Alcohol and risk of admission to hospital for unintentional cutting or piercing injuries at home: a population-based case-crossover study
Applications in articles
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Isfahan- CSC: Clinical Studies CenterBy: Tohid Jafari
Clinical features and risk factors for upper gastrointestinal bleeding in children: a case-crossover study
Applications in articles
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Isfahan- CSC: Clinical Studies CenterBy: Tohid Jafari