Add a comment about responsitivity 2

python/lsst/analysis/tools/actions/vector/calcRhoStatistics.py

@@ -382,10 +382,18 @@ def __call__(self, data: KeyedData, **kwargs) -> KeyedData:
         # chi-type ellipticity has a shear response of 2, so we need to
         # divide by 2 so that the rho-stats do not depend on the
         # ellipticity-type.
+        # Note: For distortion, the responsitivity is 2(1 - e^2_{rms}),
+        # where e_rms is the root mean square ellipticity per component.
+        # This is expected to be small and we ignore it here.
+        # This definition of responsitivity is consistent with the definions
+        # used in the rho-statistics calculations for the HSC shear catalog
+        # papers (Mandelbaum et al. 2018, Li et al., 2022).
         responsitivity = 2.0 if self.ellipticityType == "chi" else 1.0
 
         # Call the actions on the data.
         eMEAS = calcEMeas(data, **kwargs)
+        if self.ellipticityType == "chi":
+            _LOG.debug("Correction to distortion's responsitivity would be %f", 0.5 * np.abs(eMEAS) ** 2)
         eMEAS /= responsitivity  # type: ignore
         e1, e2 = np.real(eMEAS), np.imag(eMEAS)
         eRes = calcEDiff(data, **kwargs)