With this approach Ziderman concludes that “The
annual repayment burden in terms of annual income is very
light, in the region of only 2–4 percent annually” (p. 83),
and adds that “. . .the Thai student loan scheme is overly generous. . .which may be effortlessly repaid out of higher
income received on courses of schooling.” (p. 83). However,
it is clear that there are very significant dispersions of
income received by graduates around the mean ground out
by ordinary least squares earnings functions, a fact highlighted
by the relatively low explanatory power (of around
20–40%) of these models.