Association of Arsenic Exposure during Pregnancy with Fetal Loss and Infant death. A Cohort study in Bangladesh

What are the specific bias associated with this study such as Recall, Selection, Misclassification Bias to name a few.

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The study by Rahman et al. evaluated the effect of consumption of arsenic contaminated tube well water on infant death and natal loss in Bangladesh. 

There are a number of bias that may be present in any research study. These include recall bias (where there is difference between what a subject and a control recalls), misclassification bias (in simplest terms, measurement error) and selection bias (introduced when sample is not representative enough or when there is difference between exposed and control group). Cohort studies least suffer from these biases (as compared to other study designs), since subjects are chosen before hand (in a prospective study). It seems that selection bias may be present in the current case. For example, the cases of infant deaths and natal loss could have been followed more closely than non-fatal cases; although the authors state that selection and information bias have been minimized. Recall bias also has been minimized by asking the subjects to relate drinking water history to significant life events. Given the authors' efforts to minimize the bias, it is difficult to imagine any bias in this cohort study, without further information.

I would imagine that certain factors that were not included in study design, such as, history of previous natal loss or infant death, malnutrition, presence of water treatment measures, availability of medical care, etc., could have biased the results in favor of positive correlation between exposure and outcomes. Thus the systematic bias has been introduced due to study design.

Hope this helps. 

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In the article Association of Arsenic Exposure during Pregnancy with Fetal Loss and Infant: A Cohort Study in Bangladesh Is there any Recall Bias or Selection Bias and if so how does it take place in the study  what is it effect on the measure of association and why

A similar question has recently been answered (http://www.enotes.com/homework-help/association-arsenic-exposure-during-pregnancy-with-513583). The previous question dealt with the presence of any potential bias. The current question seems to be an extension of the same and I will answer the part that was not covered in the previous question. Kindly check the answer to the previous question for any bias in the study. Here I will discuss the effect of such bias on measure of association.

In the study by Rahman et al., potential recall bias may exist, since the pregnancies occurred in 1991-2000 and the water source history was collected later on. Although the authors mention that they tried to minimize such bias, it is entirely possible that subjects with negative outcomes (no infant death or fetal loss) will remember fewer details about their water source (among other details) as compared to subjects with positive outcomes (who are more likely to remember such details more clearly). This will lead to a higher degree of association between arsenic concentration and outcomes.

In the answer to the previous question, I had mentioned the potential bias due to non-inclusion of parameters such as past history of fetal loss (or infant death), availability of appropriate nutrition and healthcare, etc. A subject with a history of similar outcomes (could be totally unrelated to arsenic concentration), lack of nutrition or timely medical care will skew the study towards a positive correlation between independent variables and outcomes.

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