Question

1-The healthy worker effect is a form of what type of bias?

		Selection bias
		Observation bias
		Interviewer/recording bias
		Recall bias

2-Which of the following alternative explanations should be ruled out in order to consider a study valid?

		Bias
		Confounding
		Random error
		All of the above

3-Which of the following define bias?

		The probability that the observed result is due to "chance"
		A systematic error in the design or conduct of a study that leads to an incorrect or invalid estimate of the measure of association between the exposure and disease
		The mixing of effects between the exposure, the disease, and a third variable that distorts the relationship between an exposure and disease
		None of the above

4-Which of the following is a key fact about observation bias?

		An error that arises from systematic differences in the way information on exposure and disease is obtained from study groups
		An error that arises from systematic differences in selecting and following the study groups
		Also called control selection bias, healthy worker effect, and differential loss to follow-up
		All of the above

Answer 1

1) Healthy worker effect is a selection bias. It is a occupational related exposure.

Observation bias is a form of information bias caused by an investigator/observer incorrectly ascertaining or recording data from a participant in a study. it may occur due to observers prior knowledge about the hypothesis under investigation.

Interviewer/recording bias: it is the bias introduced by interviewer

Recall bias occurs in studies that involve self reporting, interviews. It originates as the participants cannot recall previous incident accurately and report wrong information or recall their exposure to potential risk . It is also a form of information bias

2) All of the above

Bias: It occurs due to systematic error in research methodoly, there is incorrect measure in the association between exposure and outcome. The types of bias that can occur are: selection, information, observer and recall bias. The reseracher can limit the effect of bias on the validity of study by ensuring proper design and methodology of the study

Confounding occurs when association between an exposure and outcome is distorted by the presence of another variable (confounder). Example when study aims to analyse the relation between alcohol consumption (exposure) and heart diseases (outcome), in this case smoking which is linked to both alcohol consumption and heart disaese will be a confounder. The reseracher can limit the effect of confounders on the validity of study by controlling for confounders or adequately adjusting for it in the analysis,

Random effect: it should always be considered that the findings may in fact be due to an alternative explanation or due to chance. It can be minimised but not completely avoided. It includes measurement error, samling error etc

3) Bias is defined as a systematic error in the design or conduct of a study that leads to an incorrect or invalid estimate of the measure of association between the exposure and disease

The probability that the observed result is due to "chance" is called random error

The mixing of effects between the exposure, the disease, and a third variable that distorts the relationship between an exposure and disease is called as confounding

4) Key factor about observational bias is that it is an error that arises from systematic differences in the way information on exposure and disease is obtained from study groups