  The 2D metal-insulator transition can be induced either by decreasing the
carrier density or by increasing the spin polarization by applying a magnetic
field parallel to the plane. Using experimental results for the shift in
critical carrier density in an applied field, we show that the two-electron
pair correlation function at short distance ($k_Fr\alt2$) has a universal form
along the transition line in the magnetic field-carrier density plane. This
result provides direct evidence of the central role of Coulomb repulsion and
the exchange-correlation hole in driving the metal-insulator transition.
