  In this article, the correlated basis-function (CBF) method is applied for
the first time to the quantum spin-half {\it XY} model on the linear chain, the
square lattice, and the simple cubic lattice. In this treatment of the quantum
spin-half {\it XY} model a Jastrow ansatz is utilised to approximate the
ground-state wave function. Results for the ground-state energy and the
sublattice magnetisation are presented, and evidence that the CBF detects the
quantum phase transition point in this model is also presented. The CBF results
are compared to previous coupled cluster method (CCM) results for the spin-half
{\it XY} model, and the two formalisms are then compared and contrasted.
