LANCASTER, Pa. — Conservative Amish groups have larger families than other Amish and their children are far less likely to leave the church, a trend expected to bring dramatic changes for them in the coming years, according to a book on the distinctive religious group published recently. “The Amish,” a 500-page overview of the Christian followers known for traditional dress and the use of horse-and-buggy transportation, identified 40 distinct groups and a variety of permitted practices. “They may all look alike on the outside from an external perspective, but the fact of the matter is there are over 2,000 different ways of expressing Amishness in terms of daily practice,” said co-author Don Kraybill, senior fellow at Elizabethtown College’s Young Center for Anabaptist and Pietist Studies.