percent performance levels corresponding to Alt. B [median] and Alt. B [high],
respectively, simple ratios were calculated: approximately 73 percent for Alt. B [median], approximately 83 percent for Alt. B [high].)
65 percent/60 percent X 0.67 equals and 75 percent/60 percent X 0.67 equals
As is evident from figure 8, the USPS multi-line with ZIP+4 curve (Alt. B. [low]) has an elbow in it, with no increase in the savings level occurring until ZIP+4 usage exceeds about 20 to 25 percent. USPS defends this “elbow” on the grounds that up to about 20
percent ZIP+4 usage, the read redundancy in the address
and the ZIP+4 USPS believes
code negates any that the higher
quality mail will be the first to use ZIP+4, and thus there
will be no immediate benefit a satisfactory engineering
was unable to
explanation. as multi-line
Therefore, while OTA included the elbow in the USPS-estimated curve used alternative B [low], OTA excluded the elbow for alternatives B [median] and
B [high]. For these multi-line ZIP+4 usage and savings.
For modeling purposes, OTA converted the figure 8 curves into a set of normalized linear equations using ZIP+4 usage as the independent variable and usage savings factor as the dependent variable. A usage savings factor of 1.0 equates to 100 percent of the savings projected for the single-line OCR alternative at 90 percent ZIP+4 usage. The set of curves corresponding to the linear equations is shown in figure 9. The slope of the single-line OCR curve was adjusted slightly to be consistent with the ZIP+4 sensitivity analyses included in the 1984 USPS proposal to the Postal Board of Governors (savings factors of 1.0, 0.866, and 0.72 at ZIP+4 usage rates of 0.9, 0.76, and 0.57 [corresponds to 90 percent, 76 percent, and 57 percent ZIP+4 usage]).