It was not possible for the group to conduct a detailed appraisal of the accuracy and robustness of all of the information gathered, some of which was anecdotal or qualitative in nature.
Nid oedd modd i'r grŵp gynnal arfarniad manwl o gywirdeb a chadernid yr holl wybodaeth a gasglwyd, yr oedd rhywfaint ohoni'n anecdotaidd neu'n ansoddol ei natur.