[Performance of a field test as proof of automatic cell analysis]

The screening by an automatic cell analyser (A) is justified, only if the false negative rate beta (A) is less than the false negative rate beta (M) of the manual method (M). A design is considered to get the numbers of ill persons who are "positive" by the manual method and "negative" by the automatic one, and vice versa "negative" by the manual and "positive" by the automatic. The sign test can be used to test the difference beta (A) - beta (M). Formulas for the necessary number n are given.