  Knowledge of the binary population in stellar groupings provides important
information about the outcome of the star forming process in different
environments. Binarity is also a key ingredient in stellar population studies
and is a prerequisite to calibrate the binary evolution channels. In these
proceedings we present an overview of several commonly used methods to pair
individual stars into binary systems, which we refer to as the pairing
function. Many pairing functions are frequently used by observers and
computational astronomers, either for the mathematical convenience, or because
they roughly describe the expected outcome of the star forming process. We
discuss the consequences of each pairing function for the interpretation of
observations and numerical simulations. The binary fraction and mass ratio
distribution generally depend strongly on the selection of the range in primary
spectral type in a sample. These quantities, when derived from a binary survey
with a mass-limited sample of target stars, are thus not representative for the
population as a whole.

Astrophysics