“…The answer must reside to a Sources. Trading exchange rates, national sources up to 1913, such as Carreras (1989), Lains (1995), Lazaretou (1995), Mata and Va l e rio (1994), , and, especially, cross-country quotations from Antio (1992), Posthumus (1946), Schneider and Schwarzer (1990), and Schneider et al (1993) For 1913-1938, League of Nations' Yearbooks and U S Statistical Abstract; IMF Yearbooks for The Maddison (R) column, refers to GDP per head expressed in 1990 U S dollars (at U S relative prices), computed from Maddison (1995) but revised with the latest GDP data available for each country as explained in the sources below in order to make it consistent with the new estimates Maddison's 1990 ''international dollars'' (Geary-Khamis) were previously converted into U S dollars with Maddison (1995, Table C-6) own appropriate ratios The Bairoch column derives from Bairoch (1976Bairoch ( , 1981Bairoch ( , 1989, and refers to GDP per head in 1960 U S dollars New current price estimates of GDP per head (column under Prados de la Escosura) are computed by converting product per head expressed in national currencies into U S dollars with Paasche PPPs derived from Eq (II) in Table 4 and represent real income expressed in U S relative prices (Laspeyres values) Nominal GDP estimates are (whenever possible) define at market prices per head and come from the following national sources stated below or from Mitchell (1992Mitchell ( , 1993Mitchell ( , 1994) or from OECD National Accounts and UN Yearbooks Population and trade figure are taken mainly from Mitchell (1992Mitchell ( , 1993Mitchell ( , 1994, and from the League of Nations, UN, and UNCTAD Yearbooks, unless stated in the national sources below Area surface comes from the World Almanac (1988), Cook and Paxton (1975), and, for Greece, Kostis and Petmezas (1998) National sources:…”