Statistical research on determining sensitivity of neutrinoless double beta decays

The determination of experimental sensitivity is a key step in the search for neutrinoless double beta decay ($0\nu\beta\beta$), providing a quantitative benchmark for detector design. Two commonly used statistical approaches are the counting method, which estimates sensitivity from the number of events in a predefined region of interest, and the fitting method, which extracts the signal contribution by fitting the full energy spectrum. In this work, we investigate both discovery sensitivity and exclusion sensitivity within these two approaches. Through statistical derivation and simulation verification, we show that the relative performance of the methods depends on both energy resolution and exposure, while at higher exposures the fitting method consistently yields more stringent sensitivity. These results provide guidance for selecting the optimal statistical method in future $0\nu\beta\beta$ experiments.