A/CONF.171/13 English Page 92 12.26. In the light of the persistence of significant mortality and morbidity differentials between population subgroups within countries, it is urgent to step up efforts to investigate the factors underlying such differentials, in order to devise more effective policies and programmes for their reduction. Of special importance are the causes of differentials, including gender differentials, in mortality and morbidity, particularly at younger and older ages. Increased attention should also be paid to the relative importance of various socio-economic and environmental factors in determining mortality differentials by region or socio-economic and ethnic group. Causes and trends in maternal, perinatal and infant morbidity and mortality also need further investigation. /...