Discussion:
1. Explain the difference between a highly sensitive test and a highly specific screening test. Why are highly sensitive tests more favorable?
While laboratory tests to be used in screening programs should ideally be highly accurate, most are likely to yield either false positives or false negatives. Tests may be highly sensitive, meaning that they yield few false negatives, or they may be highly specific, meaning that they yield few false positives. Many highly sensitive tests are not very specific and vice versa. For most public health screening programs, sensitive tests are desirable to avoid missing any individual with a serious disease who could be helped by some intervention. However, inexpensive, sensitive tests chosen to encourage testing of as many at-risk individuals as possible are often not very specific. When a positive result is found, more specific tests are then conducted to determine if the first finding was accurate. Most screening programs use sensitive tests and follow up positive results with more expensive tests that are both highly sensitive and highly specific. For conditions that are rare in the population being screened, the rate of false positives may be higher than the rate of true positives. Screening programs are also subject to biases, such as lead-time bias and over diagnosis bias which may make them less useful for saving lives than expected.