Estimation of a caller retrial for a telephone information rate system
Karla Hoffman, Carl M. Harris · 1986
As part of a continuing study of the usage of its Taxpayer Service Telephone Network, the U.S. Internal Revenue Service wished to determine more accurate methods for demand measurement. It has long been recognized that the total number of calls coming into such a busy telephone system overesti- mates the actual number of distinct callers. The Service had previously estimated its real demand by adding (3) of both the number of blocked or overflow calls and the number of abandonments to the total actually answered. The thrust of this current study then was to develop an accurate statistical method for providing a more objective formula for this true demand, which turns out to be equivalent to estimating the probability of retrial by blocked and abandoned callers. The major result which has come from this effort is that the average daily retrial percentage taken across location and time of year seems to be moderately stable about a mean value of 69%, somewhat dependent on both location and (particularly) time of year. The value is consistently higher during periods close to important filing milestones and lower otherwise. We show this to mean that, whenever a rate of 69% is used, the actual demand would be estimated by augmenting completed loads by 31% of the number of blocked and abandoned calls for the period of concern. A toll-free telephone system has been estab- lished by the U.S. Internal Revenue Service (IRS) to permit taxpayers to obtain tax assistance in a timely and inexpensive manner. The IRS covers the Continental United States by means of a number of strategically located answering sites, which can be reached for a charge no more than that of a local call. The efficient management of these Taxpayer Information Centers is a very dif- ficult problem at best, but it has been hoped that rational approaches can be developed for the nec- essary resource requirement decisions. The prob- lem of modeling this system was introduced in Harris, Hoffman and Saunders (1984), which portrays the initial simulation study of the IRS network by the Center for Applied Mathematics