A 33-year-old woman comes to the clinic for a routine health maintenance examination. She has no lower abdominal pain, vaginal bleeding, or vaginal discharge. Her past medical history is remarkable for 1 episode of uncomplicated urinary tract infection treated with a short course of antibiotics. She is currently not taking any medications. She has had 5 sexual partners in her life and has used barrier contraception the majority of the time. Her latest sexual relationship began 3 months ago. Her last cervical cancer screening examination was a Pap smear performed at the age of 23 that showed no abnormalities. She does not use tobacco, alcohol, or illicit drugs. During her visit, she requests screening for cervical cancer and appears extremely concerned as her older sister was recently diagnosed with it. During the study, women with abnormal Pap test results or a positive HPV test underwent colposcopy and biopsy, as did a random sample of women with negative test results. The purpose of performing a colposcopy and a biopsy on women with negative test results is to reduce which type of bias?

Question

A 33-year-old woman comes to the clinic for a routine health maintenance examination.  She has no lower abdominal pain, vaginal bleeding, or vaginal discharge.  Her past medical history is remarkable for 1 episode of uncomplicated urinary tract infection treated with a short course of antibiotics.  She is currently not taking any medications.  She has had 5 sexual partners in her life and has used barrier contraception the majority of the time.  Her latest sexual relationship began 3 months ago.  Her last cervical cancer screening examination was a Pap smear performed at the age of 23 that showed no abnormalities.  She does not use tobacco, alcohol, or illicit drugs.  During her visit, she requests screening for cervical cancer and appears extremely concerned as her older sister was recently diagnosed with it. During the study, women with abnormal Pap test results or a positive HPV test underwent colposcopy and biopsy, as did a random sample of women with negative test results.  The purpose of performing a colposcopy and a biopsy on women with negative test results is to reduce which type of bias?

Quizplus · Accepted Answer

Explanation: Ideally, gold standard testing would be performed in all participants; however, this may not be feasible due to ethical, time, and cost concerns, particularly if the gold standard method is invasive and associated with an increased risk of complications. For example, in a study of a new screening test for a certain liver condition where liver biopsy is the gold standard, it may not be feasible to perform a biopsy on all patients, particularly those who have a negative result on the new screening test. Such a situation can cause verification bias, or workup bias, a type of measurement bias that occurs when a study uses gold standard testing selectively in order to confirm a positive (or negative) result of preliminary testing; this can result in overestimates (or underestimates) of sensitivity (or specificity). A possible method to reduce verification bias is to perform gold standard testing in a random sample of participants with negative results, as seen in this study on cervical cancer. The results from this analysis can be used to extrapolate the likely number of cases that would have been found if all participants with negative screening tests had been fully investigated with gold standard testing. (Choice A) Contamination bias occurs when the control group unintentionally receives the treatment or the intervention, thereby reducing the difference in outcomes between the control and treatment group. (Choice B) Observer bias occurs when an observer responsible for recording results is influenced by prior knowledge about participants or study details. Blinded studies (as in this case) usually avoid this bias by preventing observers from knowing which treatment or intervention the participants are receiving; this leads to a more objective measurement of outcomes. (Choice C) Selection bias results from the manner in which study participants are selected or lost to follow-up. Randomization in a clinical trial reduces selection bias. (Choice D) Susceptibility bias is a type of selection bias where experimental and control groups differ from a prognostic standpoint, possibly due to unforeseen confounding variables. Patients in this trial were randomly selected for a specific screening method, minimizing this type of bias. Educational objective: Verification bias occurs when a study uses gold standard testing selectively in order to confirm a positive (or negative) result of preliminary testing. This can result in overestimates (or underestimates) of sensitivity (or specificity). References: Correcting for verification bias in studies of a diagnostic test's accuracy. (http://www.ncbi.nlm.nih.gov/pubmed/9871951)

A 33-Year-Old Woman Comes to the Clinic for a Routine