Recently, along with diminishing numbers of students, it has been observed
that some graduate programs still have lots of students, whereas other fiel
ds of study suffer from a great loss of students. Apparently, students do n
ot distribute evenly over the fields that a university offers. The relation
s among the number of students in different fields of concentration are not
constant. In particular, the harder subjects appear to suffer more from a
diminishing number of students than the fields with a reputation of being s
omewhat "softer."
The reasons for such trends must be expected to be related to the size of t
he market, and to psychological effects. Our study has been motivated by at
tempts to model economic mechanisms that are related to advertising [Feicht
inger, 1992]. We have constructed a mathematical model that is able to expl
ain trends such as reported above.