Cancer screening: Between appropriateness and effectiveness.

Two similar words, effectiveness and efficacy, have comparable insight and nearly describe analogous meaning for a screening test, yet clear understanding and perception of their diverse meanings will help clarify the basis of the differing conclusions about whether screening tests for different cancers reduce morbidity and mortality. Screening test may not be effective even when it sounds to be efficacious, on the other hand it should be efficacious when the test is effective.