There is a great new article in the Spring edition of the International Journal of Frontier Mission by James Bultema, who has done some very interesting research on the Protestant Church in Turkey. There were two large growth spurts and this is how he accounts for them:
During these four and half decades [1960-2005], you see one period—from 1988 to 1994—that towers over other periods with respect to the growth rate. The reason for that spike in growth is quite simple: the New Testament in modern Turkish was printed and distributed, beginning in mid 1987. We had another spike from 2000-2002, and that is because the whole Bible in modern Turkish was first printed and distributed at the beginning of that period. (Bultema 2010: 28)
Check it all out over at www.ijfm.org.