  Correlation functions measured as a function of $\Delta \eta, \Delta \phi$
have emerged as a powerful tool to study the dynamics of particle production in
nuclear collisions at high energy. They are however subject, like any other
observables, to instrumental effects which must be properly accounted for to
extract meaningful physics results. We compare the merits of several techniques
used towards measurement of these correlation functions in nuclear collisions.
We discuss and distinguish the effects of finite acceptance, and detection
efficiency that may vary with collision parameters such as the position of the
event in the detector and the instantaneous luminosity of the beam. We focus in
particular on instrumental effects which break the factorization of the
particle pair detection efficiency, and describe a technique to recover the
robustness of correlation observables. We finally introduce a multi-dimensional
weight method to correct for efficiencies that vary simultaneously with
particle pseudo rapidity, azimuthal angle, transverse momentum, and the
collision vertex position. The method can be generalized to account for any
number of "event variables" that may break the factorability of the pair
efficiency.
