The fact that different research teams using different datasets and different methods have found the Population Y signal at different intensities — or have sometimes appeared not to find it at all — is one of the most important aspects of the scientific debate and deserves careful explanation.

Several factors can produce variation in the results of ancient genome analyses when applied to questions like Population Y.

The composition of the reference panel — the set of modern and ancient genomes used as comparison populations in the statistical tests — can significantly affect the results.

If the reference panel includes populations that carry the signal themselves, or if it omits populations that would help calibrate the baseline expectations, the results of the statistical tests will be affected.

Different research teams have used different reference panels, and this methodological difference is one source of variation in reported results.