A geneticist is interested in the potential causes of a congenital abnormality. She hypothesizes that acetaminophen use during the first trimester of pregnancy might be associated with the abnormality. In her study, a sample of mothers of children with and without the abnormality are randomly selected from government birth records. Personal interviews are then conducted with the mothers to determine fetal exposure to acetaminophen. Results show that mothers of children who do not have the abnormality did not take acetaminophen as frequently during the first trimester. This type of study is most susceptible to which of the following types of bias?
Recall bias results from study participants' inaccurate recall of past exposure and occurs most often in retrospective studies such as case-control studies. People who have experienced an adverse event (eg, congenital abnormalities in their children) are more likely to recall previous potential risk factors (eg, acetaminophen use) than people who have not experienced an adverse event.
Contrary to case-control studies, which evaluate exposure to potential risk factors retrospectively, prospective studies begin with exposed and unexposed individuals. Because the exposure status is determined at the time of enrollment in the study, recall bias is minimized.
(Choice A) Allocation bias can result from the way patients are assigned to the treatment and control groups. It may occur when subjects are nonrandomly assigned to the study groups of a clinical trial (eg, physicians may preferentially enroll sicker patients into the experimental group). Allocation bias is different from selection bias, which occurs when the studied sample does not represent the general population (eg, because of nonrandom selection).
(Choice B) Detection bias refers to the fact that a risk factor itself may lead to extensive diagnostic investigation and increase the probability that a disease is identified. For instance, patients who smoke may undergo increased imaging surveillance due to their smoking status, which would detect more cases of cancer in general.
(Choice D) Referral (admission rate) bias occurs when the case and control populations differ due to admission or referral practices. For instance, a study involving asbestos as a risk factor for lung cancer conducted at a hospital specializing in treating asbestosis may select patients with lung cancer (cases) from the respiratory department and a control group without lung cancer from other departments. Because the hospital specializes in asbestosis treatment, patients in the respiratory department with lung cancer are more likely to have a history of asbestos exposure (compared to patients with lung cancer at other, nonspecialized institutions). Therefore, the study may erroneously report a stronger association than actually exists.
(Choice E) Selection bias occurs when the method of selection used in a particular study results in selection sample of participants who are not representative of the intended population. A common example is patients with cancer who fail standard therapy and who are therefore the most likely to enroll in experimental trials (self-selection), leading to results that are not applicable to patients with less advanced cancers.
Educational objective:
Recall bias results from study participants' inaccurate recall of past exposure and occurs most often in retrospective studies such as case-control studies. People who have experienced an adverse event are more likely to recall risk factors than those who have not experienced an adverse event.