Roberts was Director of Health Policy at the International Rescue Committee. In 1994 he worked in Rwanda for the World Health Organization, and performed a similar study to estimate the number of Rwandan refugees. In 2000, he performed a similar study which estimated 1.7 million deaths due to the war in the Democratic Republic of Congo. This study was cited in a U.N. Security Council resolution that all foreign armies must leave Congo, a United Nations request for $140 million in aid, and a pledge by the US State Department for an additional $10 million in aid.