  Half life values for $\alpha$-decay in the mass region $A=150-200$ have been
calculated in the Microscopic Super Asymmetric Fission Model. The interaction
between the $\alpha$-particle and the daughter nucleus has been obtained in the
double folding model with the microscopic interaction DDM3Y1. Theoretical
densities for the nuclei involved have been calculated in Relativistic Mean
Field approach with the Lagrangian density FSU Gold. Spectroscopic factors for
$\alpha$-decay, calculated as the ratios of the theoretically calculated and
experimentally measured half life values, show a simple dependence on the mass
number and the product of the number of valence protons and neutrons. The
implications of the parameterization have been discussed. Finally, based on
this simple relation, $\alpha$-decay half life values in a number of nuclei
have been predicted.
