according to historian norman davies the polish census of 1931 listed the nationalities by language as polish, 69% of the population, ukrainian, 15%, jews 8.5%, belarusian, 4.70%, german, 2.2%, russian 0.25%, lithuanian, 0.25%, czech 0.09%, norman davies included the ruthenians with the ukrainians however the polish census figures list them as separate group with 3.82% of the population. the classification of the ethnic groups in poland during the second polish republic is a disputed topic, tadeusz piotrowski maintains that the 1931 polish census "involved questionable methodology, especially the use of mother tongue as an indicator of nationality", noting that it had underestimated the number of non-poles. the official figures for nationality from the 1931 polish census based on the mother tongue put the percentage of ethnic poles at 68.9%, jews 8.6% and other minority groups 22.5%., piotrowski cited a study by the polish historian jerzy tomaszewski that puts that the adjusted census figures(taking religious affiliation into account) of ethnic poles at 64.7%, jews 9.8% and other minority groups 25.5% of poland's population. polish demographer piotr eberhardt maintains that it is commonly agreed that the criterion of declared language to classify ethnic groups led to an overestimation of the number of poles in pre-war poland. he notes that in general, the numbers declaring a particular language do not mesh with the numbers declaring the corresponding nationality. members of ethnic minority groups believe that the language criterion led to an overestimation of poles.