  A long spin relaxation time (tausf) is the key for the applications of
graphene to spintronics but the experimental values of tausf have been
generally much shorter than expected. We show that the usual determination by
the Hanle method underestimates tausf if proper account of the spin absorption
by contacts is lacking. By revisiting series of experimental results, we find
that the corrected tausf are longer and less dispersed, which leads to a more
unified picture of tausf derived from experiments. We also discuss how the
correction depends on the parameters of the graphene and contacts.
