Per cent of predicted as the limit of normal in pulmonary function testing: a statistically valid approach.

Per cent of predicted as the limit of normal in pulmonary function testing: a statistically valid approach It has been traditional in pulmonary function testing to set the limits of normal as the predicted -4-20%. Since most pulmonary function tests, and all spirometric tests, are abnormal only when below predicted, the rule of thumb for the limit of normal becomes 80% of predicted. How this