The characteristics of power systems are altered by the high penetration level of inverter-based resources (IBRs). Several short circuit ratio (SCR) variants have been developed by industrial and academic communities to accommodate IBR interactions. These variants are distinguished by diverse formulations, indication performance, and information requirements. In this paper, a comparative analysis of SCR variants is carried out in terms of voltage stability indication. The assumptions required to guarantee accurate indication are derived by comparing the variant formulations with a theoretical voltage stability boundary. The necessary information for the variants is clarified to elucidate the calculation difficulty. The comparison analysis contributes to a better understanding of the limitations of these variants. Finally, the effectiveness of the comparison analysis is demonstrated on a modified IEEE 39-bus benchmark system.