Hi Juan,

It does happen. Many studies are conducted in secondary care and their results cannot be transferred to primary care for this reason. For example, one study of the Well’s criteria for DVT found: "Sensitivity, specificity, and negative predictive value were substantially lower than in the original [Well’s et al] study.”

Ref Oudega R, Hoes AW, Moons KG. The Wells rule does not adequately rule out deep venous thrombosis in primary care patients. Ann Intern Med. 2005;143(2):100-107.

Kev Hopayian

On 2 Feb 2015, at 14:01, Juan Acuna <[log in to unmask]> wrote:

Due to the way they are calculated, the study to definitely prove if Sn/Sp change with prevalence (beyond mock calculations and simulations) is probably undoable (or at least I have never seen it).