(New York Times) — It has long been the standard practice in medical testing: Give drug treatment to one group while another, the control group, goes without. Now, New York City is applying the same methodology to assess one of its programs to prevent homelessness. Half of the test subjects — people who are behind on rent and in danger of being evicted — are being denied assistance from the program for two years, with researchers tracking them to see if they end up homeless. The city’s Department of Homeless Services said the study was necessary to determine whether the $23 million program, called Homebase, helped the people for whom it was intended. Homebase, begun in 2004, offers job training, counseling services and emergency money to help people stay in their homes.