similar non-certified buildings. Buildings certified under LEED do not have to prove energy or water efficiency in practice to receive LEED certification points, but instead LEED uses modeling software to predict future energy use based on intended use. This has led to criticism of LEED's ability to accurately determine the efficiency of buildings. The USGBC has noted that "Buildings have a poor track record for performing as predicted during design." Energy performance research In 2009, architectural scientist Guy Newsham (et al.) of the National Research Council of Canada (NRC) analyzed a database of 100 LEED certified (v3 or earlier version) buildings. In this study, each building was paired with a conventional "twin" building within the Commercial Building Energy Consumption Survey (CBECS) database according to building type and occupancy. On average, LEED buildings consumed 18 to 39% less energy by floor area than the conventional buildings, although 28 to 35% of LEED-certified buildings used more energy. The paper found no correlation between the number of energy points achieved or LEED certification level and measured building performance. In 2009 physicist John Scofield published an article in response to Newsham et al., analyzing the same database of LEED buildings and arriving at different conclusions. Scofield criticized the earlier analysis for focusing on energy per floor area instead of a total energy consumption. Scofield considered source energy (accounting for energy losses during generation and transmission) as well as site energy, and used area-weighted energy use intensities (EUIs) (energy per unit area per year), when comparing buildings to account for the fact that larger buildings tend to have larger EUIs. Scofield concluded that, collectively, the LEED-certified buildings showed no significant source energy consumption savings or greenhouse gas emission reductions when compared to non-LEED buildings, although they did consume 10–17% less site energy. In 2013 Scofield analyzed 21 LEED-certified buildings in New York City. He found that LEED-Gold buildings used 20% less source energy while Silver and Certified buildings used 11 to 15% more source energy, on average, than did their conventional counterparts. In 2014, architect Gwen Fuertes and engineer Stefano Schiavon developed the first study that analyzes plug loads using LEED-documented data from certified projects. The study compared plug load assumptions made by 92 energy modeling practitioners against ASHRAE and Title 24 requirements, and the evaluation of the plug load calculation methodology used by 660 LEED-CI and 429 LEED-NC certified projects. They found that energy