Toward the end of his career, Coale became interested in the population changes in China and understanding the fertility transition there as well as factors affecting the sex ratio at birth. In a 1986 study he conducted, India and China were compared in both their population size and fertility trends. A survey named the "1/1000 Fertility Survey" reached out to women living in various provinces of China and asked them to relate a brief history of their marital status and a family planning discussion. The survey contributed to an understanding of the population and fertility changes that would occur in China shortly after. Published in a Journal article called "Population trends in China and India", Coale introduced the possible causes of differences in fertility trends in such highly populated countries. These reasons are based on policies put in place to reduce birth rates as well as some cultural differences that come into play. Finally, Coale presents the future of both countries and states that despite the efforts to reduce birth rates, the countries will remain the most populated.