1991
The assumption that the cost to the user associated with a certain retrieval
time is linear in that time is wildly innaccurate. The real function could
be very dependent on circumstances (like go to infinity at a deadline).
A better general approximation might be logarithmic for large time delays,
and linear for small ones, like a*log(b*t-1) which has two parameters.
Note: The cost of retrieval time