Pew Forum suggests that the growth in Islam in the past 10 years is related to the birth rate. Growth will slow as the birth rate slows in countries with large Muslim populations. They suggest that the conversion rate is effectively nil as converts to Islam equal the number leaving Islam.
A 2001 study by David Barrett suggests that the conversion rate to Christianity is twice the rate of Islam.
A summary of 3 studies in 40 countries over 10 years, ending 2001, finds:
52,557 people surveyed said they used to be Christian (Catholic, Protestant, Orthodox) but only 48,588 say they are currently Christian; a change of -8%.
458 people surveyed said they used to be Muslim and 485 say they now are; a change of +6%.
The biggest change is the loss of former Christians to "no religious affiliation" at a rate of approximately 20% and an overall growth rate of 50% 'conversions'.
