a mixture of selection bias and confounding (checkoway et al 1989, li & sung 1999) mixture of...
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![Page 1: A mixture of selection bias and confounding (Checkoway et al 1989, Li & Sung 1999) Mixture of biases?](https://reader035.vdocuments.site/reader035/viewer/2022062301/5697bfe21a28abf838cb441d/html5/thumbnails/1.jpg)
A mixture of selection bias and confounding
(Checkoway et al 1989, Li & Sung 1999)
Mixture of biases?
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A
Exposed
What is the ideal reference?
t0 t1
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A
Exposed
t0 t1
A
Unexposed
t1t0
What is the ideal reference?
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(Miettinen 1988)
HWE is a comparison problem
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Components of HWE
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Healthy hire effect
(Arrighi & Hertz-Picciotto 1994, Checkoway et al 1989)
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Healthy worker survivor effect
HWE occurs because of differential survival of workers with different risk of disease at work with the same exposure(Arrighi & Hertz-Picciotto 1994, Checkoway et al 1989)
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The length of time the population has been followed (time-since-hire)
HWE is strongest during active employment and rapidly disappear following the cessation of employment.
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Monson (1986) divided the follow-up into two phases; a dynamic phase and a stable plateau
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Beneficial effect of work
Improved access to health care Routine disease screening Physical exercise
(Doll 1988)
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Factors affecting HWE
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Time related factors
Age at hire Age at risk Duration of employment
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Age at hire
Workers with high age at hire will show strong HWE: RR for all causes of mortality, according to Fox & Collier (1976) (Checkoway et al 1989)
Age at hire 25-44 45-54 55-64 65-74
0.45 0.37 0.32 0.23
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Age at risk Workers with high age at risk will show low
HWE: RR for all causes of mortality by age at risk
(Checkoway et al 1989)
Study Age at risk <55 55-64 65-74 >75
Fox and Collier(1976) 0.64 0.79 0.96 0.60McMichael et al (1976) 0.81 0.89 0.95 1.13Delzell and Monson (1981) 0.80 0.90 0.90 1.00
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Age at risk (McMichael 1974)
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Duration of employment
The decrease in mortality is more obvious in the longest employment duration categories
(Baillargeon & Wilkinson 1999)
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Disease entity
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Socioeconomic status
The HWE is stronger in more qualified jobs
(Axelson 1988)
Professional workers demonstrate a stronger overall HWE
(Baillargeon & Wilkinson 1999)
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Gender
The effect is stronger for females than males (Howe 1988)
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Avoiding HWE
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Identify the correct external comparison group, or a
representative sample of it
(McMichael 1987)
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A number of Authors have suggested to assemble a large group of employed persons and use their mortality rates as a standard basis for external comparison
(Monson 1986)
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Progress from external comparisons to internal comparisons
(McMichael 1987)
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Start the study after a latency time (lag)
(McMichael 1987)
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Trace and include those individuals who leave the workforce before retirement
(McMichael 1987)
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A
Exposed
t0 t1
A
Unexposed
t1t0
Conclusion: the core of the HWE is lack of an ideal
reference
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Summary & Conclusion
HWE is caused by inadequate reference group (i.e., a comparison problem)
(Miettinen 1988) HWE is a complex and problem creating
bias, it comprises several factors, and may be modified by a number of factors
(McMichael 1974) It is not possible to make
generalizations in a particular case of HWE (Geoffrey 1989)