PRINCETON, NJ -- This Christmas season, 78% of Americans identify with some form of Christian religion, a proportion that has been declining in recent decades. The major reason for this decline has been an increase in the percentage of Americans claiming no religious identity, now at 13% of all adults. The trend results are based on annual averages of Gallup's religious identity data in America that stretch back over 60 years. One of the most significant trends documented during this period is the substantial increase in the percentage of American adults who don't identify with any specific religion. In 1948, only 2% of Americans did not identify with a religion. That percentage began to rise in the late 1960s and early 1970s. Eleven years ago, in 1998, 6% of Americans did not identify with a religion, a number that rose to 10% by 2002. This year's average of 13% of Americans who claim no religious identity is the highest in Gallup records.