Although the Derjaguin-Landau-Verwey-Overbeek (DLVO)-screened Coulomb pair interaction potential was derived under restricted theoretical conditions, its current usage on real systems tends to ignore these constraints, and consequently, the concepts of "effective charge", "effective screening parameter", and even "effective radius" have been championed in order to maintain the intrinsic DLVO mathematical form. The screened Coulomb expression is examined critically vis-A-vis the effective screening parameter for a charge stabilized colloidal suspension under salt-free conditions. Because the ion concentration under actual experimental conditions is usually unknown, or at best not reported, we simulate the experimental data by means of accurate Monte Carlo simulation methods, which enables one to control both the charge on the macroion and the microion concentration in the computation cell. These data are then fit to the standard Yukawa potential for the macroion as employed in the DLVO theory. It is seen that at low to moderate macroion charge (less than or equal to400 \e\ for monovalent counterions, less than or equal to150 \e\ for divalent counterions) a "single" screened pairwise interaction between the macroion and the counterion is adequate. However, such analysis fails significantly for highly charged macroions.