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General issues of Vaccine
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General issues of Tropical med.
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General issues of Travel med.
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Trematode (fluke, distoma)
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Three mechanisms (assumptions) of data missing
Mechanisms (assumptions) of data missing
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Description
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[*Example] A cohort study in which participants report their body weight every week to research center for 52 weeks in total
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Missing not at random MNAR
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- Missing depends on observed data
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- Some participants intentionally deny to report higher body weights they don't like and only report lower body weights they like
- Data of those participants are missed because of the values in the variable body weight themselves
- Researchers cannot explain/predict the missing mechanism by
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Missing at randam MAR
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- Missing does not depend on unobserved data, but may depend on observed data
- The cause of missing can be explained by
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- 15% of female participants deny to report their body weights after the agreement regardless of measured body weights, but only 1% of male deny to report:
- Data of female participants are more likely missed not because of data (body weights) themselves but because female are more likely reluctant to report their body weights
- In other words, values in the variable body weight themselves do not affect the missing but another variable sex affects the missing of values in the variable body weight
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Missing completely at random MCAR
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- Missing does NOT depend on observed data NOR on unobserved data
- Missing occurs purely at random independely from any observed and unobserved data
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- A participant moves to outside cohort area because of family affair which has nothing to do with the study and is lost to follow up at the 10th week:
- Data after the move are missed not because of data (body weights) themselves, nor because of the participant's unobserved (unmeasured) characteristic related to the study
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