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