MSFinals-6016

MSFinals-6016

A new biomarker test is developed to detect breast cancer at early stages. The company that developed the test conducted a randomised study to compare the new test to the current standard of care – mammography – among women over 40. They concluded that breast cancer patients whose cancer was identified by the biomarker lived, on average, 1.5 years longer than those whose cancers were identified by mammography. Subsequently, additional independent studies showed that there was truly no difference in survival between the two groups.

Which of the following biases is most likely to have occurred?