Introduction to Case-crossover design · Expo Unexpo Hazard period Exposed a b Unexpo c d Controls...

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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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.


Why call it Case-Crossover?

each case is its own controlviewed retrospectively

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Starting example

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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


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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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.


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Despite being similar, previous experience in conducting case-control studies

does not fully prepare you for doing case-crossover study.


Terminology used in case-crossover

design

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- Case window, or current period, or effect period:

Example

Terminology

✍Exposure A

Effect period

Exposure B Effect period


-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


The length of this period is very important

Terminology

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- 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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Suitable study cases

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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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Pros and Cons

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Pros:

Pros and cons

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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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Applications in articles

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A case-crossover study of alcohol consumption, meals and the risk of road traffic crashes


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The role of alcohol and drugs in triggering criminal violence: a case-crossover study


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Risk of new acute myocardial infarction hospitalization associated with use of oral andparenteral non-steroidal anti-inflammation drugs


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Alcohol and risk of admission to hospital for unintentional cutting or piercing injuries at home: a population-based case-crossover study


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Clinical features and risk factors for upper gastrointestinal bleeding in children: a case-crossover study


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Introduction to Case-crossover design · Expo Unexpo Hazard period Exposed a b Unexpo c d Controls...

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