We've been through this before, campers...
Let's use these numbers- for four year private programs, they are a reasonable estimate. For state schools, apply whatever uniform discount rate you wish.
Cost of education, year one: $40,000
Cost of education, year two: $40,000
Cost of education, year three: $40,000
Cost of education, year four [APPE year]: $16,000
Now, a school could charge the face value amounts listed above, and offer a discount to the PY4's.
OR, a school could average the cost over all four years and charge the mean cost per year (in this instance, $34,000 per year times four years). Sure, the PY4 year doesn't cost $34k...but then again neither do the PY1-PY3 years. Most schools do this- the PY4 tuition is used to subsidize the PY1-PY3 tuition.
Schools like Pacific that offer a last year discount are the exception; so are the two Philly schools (USP and Jefferson), which charge a HIGHER tuition for the PY4 year.