In Poland, religious freedom is guaranteed by the 1997 Constitution and by international instruments incorporated into Polish law. The country is also party to most European and universal human rights documents. In 2003, the number of Catholics was estimated at 34,443,998 (90.1 % of the entire population), the number of Orthodox Christians at 510,712 (1.34 %) and the number of Protestants at 162,102 (0.42 %). Surveys of the Centre of Public Opinion Research (CBOS) and the Catholic Church Institute of Statistics have shown that 90 % of the Polish population consider themselves a religious person, whereas the latest CBOS survey (2015) reveals that 50 % of the population participates in mass at least once a week (58 % in 2005). The same survey indicates that the proportion of people who do not attend Church services has increased from 9 % in 2005 to 13 % in 2015. Daily prayer is also in steep decline: from 66 % in 2005 to 43 % in 2015.