TRENDS

Since the late 19th century the demographics of religion have changed a great deal. Some countries with a historically large Christian population have experienced a significant decline in the numbers of professed active Christians. Symptoms of the decline in active participation in Christian religious life include declining recruitment for the priesthood and monastic life, as well as diminishing attendance at church. At the same time, there has been an increase in the number of people who identify themselves as secular humanists. In many countries, such as the People's Republic of China, communist governments have discouraged religion, making it difficult to count the actual number of believers. However, after the collapse of communism in numerous countries of Eastern Europe and the former Soviet Union, religious life has been experiencing resurgence there, particularly in the forms of Neopaganism and Far Eastern religions.
Following is some available data based on the work of World Christian Database and its predecessor, the World Christian Encyclopedia. While controversial in some respects, the results have been studied and found "highly correlated with other sources of data" but "consistently gave a higher estimate for percent Christian in comparison to other cross-national data sets" according to a study published in the Journal for the Scientific Study of Religion.