  The application of the collective variables method to the study of the
behaviour of nonuniversal characteristics of the system in the critical region
is illustrated by an example of the order parameter. Explicit expressions for
the order parameter (the average spin moment) of a three-dimensional uniaxial
magnet are obtained in approximations of quartic and sextic non-Gaussian
fluctuation distributions (the \rho^4 and \rho^6 models, respectively), taking
into account confluent corrections. Some distinctive features appearing in the
process of calculating the order parameter on the basis of two successive
non-Gaussian approximations are indicated. The dependence of the average spin
moment of an Ising-like system on the temperature and microscopic parameters is
studied.
