Juvenile/Adult Ratio (JA) The JA is the ratio of children 5-14.9 years of age to adults over the age of 20 years (5-14,9/20+) Jackes 1992: 215, 1994:176). This ratio of deaths reflects fertility because as fertility increases the number of juvenile deaths relative to adult deaths also increases Jackes 1994:176). Using the data in the life table, the JA ratio in the Ban Chiang skeletal series is 0.103 (10/97.02) that is, juvenile deaths are approximately 10% of adult deaths, a low proportion suggesting low fertility.