We discuss the variation of cosmological upper bounds on M _ { \nu } , the sum of the neutrino masses , with the choice of data sets included in the analysis , pointing out a few oddities not easily seen when all data sets are combined .
For example , the effect of applying different priors varies significantly depending on whether we use the power spectrum from the 2dFGRS or SDSS galaxy survey .
A conservative neutrino mass limit of M _ { \nu } < 1.43 eV ( 95 % C.L . )
is obtained by combining the WMAP 3 year data with the cluster mass function measured by weak gravitational lensing .
This limit has the virtue of not making any assumptions about the bias of luminous matter with respect to the dark matter , and is in this sense ( and this sense only ) bias-free .