of the total income tax (8% in Baden-Württemberg). Many members choose not to formally register to their church anymore in order to have lighter taxes, since those who opt out aren't obligated to pay the additional church surtax. According to a study, approximately 44% of the persons who unregistered from their church in 2018 did so in order to avoid paying the church tax. According to a 2017 study by the Pew Research Center, around 20% of people who are not registered to any church nonetheless consider themselves Christians. Therefore, the official church count may underestimate the actual number of people who consider themselves as Catholic or Protestant, as noted by the 2011 Census, which provides comparable data on the religious statistics based on self-identification and the church register. According to these church stats, Christianity is the largest religious group in Germany, with around 44.9 million adherents (53.9%) in 2020 of whom 22.2 million are Catholics (26.7%) and 20.2 million are Protestants (24.3%). According to other estimates, Orthodox Christianity has 1.6 million members or 1.9% of the population. Other minor Christian religions counted together have approximately 0.8 million members, forming 1.1% of the total population. The second largest religion in Germany is Islam, with around 2.9–4.7 million adherents (3.5–5.7% of the population), almost all of whom have full or partial foreign background. Smaller religious groups include Buddhism (0.2–0.3%), Judaism (0.1%), Hinduism (0.1%), Yazidis (0.1%) and others (0.4%). At the end of 2020, 33.8 million or 40.7% of the country's population were not affiliated with any church or religion. Demographers estimate that in Germany there are around 100,000 religious Jews (Judaism), and a further 90.000 ethnic Jews with no religion, around 100,000 Yazidis, 130,000 Hindus, and 270,000 Buddhists. Survey data In 2017, a survey conducted by Pew Research Center found that 71% of German adult population consider themselves Christians when asking about their current religion (irrespective of whether they are officially members of a particular Christian church). The same survey shows that most of Christians in Germany are non-practicing (defined as people who identify as Christians, but attend church services no more than a few times per year). 5% of people questioned state they have a non-Christian religion and 24% are of no religion. In 2016, the German Politbarometer, found that 34.2% of the adult population entitled to vote were Protestants, 31.9% were Catholics, 28.8% were unaffiliated, 2.5% were Muslims, 0.02%