Complex sentence: In addition, the studies claim that the rate of abuse by priests had fallen sharply in the last twenty to thirty years, and that some 75% of the cases in the United States occurred between 1960 and 1985.
Split into simpler sentences: In addition, the rate of abuse by priests had fallen sharply in the last twenty to thirty years. Some 75% of the cases in the United States occurred between 1960 and 1985.