For starters, the sample size of the study is 130 people. In a country of 175 million, that is just not representative. 130 respondents isn't representative even of the 800,000 or so people in the Federally Administered Tribal Areas (FATA), the region of Pakistan where most drone strikes occur. Moreover, according to the report's methodology section, there is no indication of how many respondents were actual victims of drone strikes, since among those 130 they also interviewed "current and former Pakistani government officials, representatives from five major Pakistani political parties, subject matter experts, lawyers, medical professionals, development and humanitarian workers, members of civil society, academics, and journalists."
James Cavallaro and Sarah Knuckey, two of the study's authors, want more transparency:
Today, it is almost impossible to have an informed public debate about U.S. policies on drone warfare – primarily because of efforts by the government to shield its targeted killings program from democratic accountability. The U.S. should release Department of Justice memorandums outlining the legal basis for targeted killings, make public critical information about U.S. policies, ensure independent investigations into drone strike deaths (with prosecutions, as appropriate) and establish compensation programs for affected civilians.