Not using age specific values invalidates study

EDITOR,--J Fletcher and colleagues' paper does little to help purchasing authorities when they have to decide which screening programme and screening policy to choose when introducing screening for Down's syndrome.1 While the methodology used in the paper is valuable when used correctly, the authors were wrong to apply the overall sensitivity and specificity of serum testing obtained from whole population data rather than using age specific values. They argue that “this was done to reduce complexity.” As a consequence of their not making allowance for the fact that in older women (those over …