Read this article and answer this question Currently, there is no official census of religion in Russia, and estimates are based on surveys only. In 2012 the research organization Sreda published Arena Atlas, a detailed enumeration of religious populations and nationalities in Russia, based on a large-sample country-wide survey. They found that 46.8% of Russians declared themselves Christians (including 41% Russian Orthodox, 1.5% simply Orthodox or members of non-Russian Orthodox churches, 4.1% unaffiliated Christians, and less than 1% for both Catholic and Protestant), while 25% were spiritual but not religious, 13% were atheists, 6.5% were Muslims, 1.2% were followers of "traditional religions honoring gods and ancestors" (including Rodnovery, Tengrism and other ethnic religions), and 0.5% were Tibetan Buddhism. However, later that year, the Levada Center estimated that 76% of Russians were Christians, and in June 2013, the Public Opinion Foundation estimated that 65% of the population was Christian. These findings are in line with Pew Research Centers 2011 estimate that 73.6% of Russians were Christians, with Russian Public Opinion Research Center (VCIOM)s 2010 survey (~77% Christian), and with Ipsos MORIs 2011 survey (69%).
Which study labeled the smallest number of Russians as Christian?
Arena Atlas