Consider a message with one binary characteristic which would occur in a
noiseless informative process transmitting a single bit. The characteristic occurs
with probability (and average frequency) ; in messages to be passed (referred to
as relevant messages) and probability (and average frequency) < in all messages
[Los98]. If a filter attempts to pass only those messages at or above the average
position of relevant messages in a list of messages ordered by decreasing relevance,
the percent of all messages that will be passed is .= .";>*/