Actually I was practicing for my English writing test, and I'm not sure whether such usage is correct. Any help will be appreciated.
As described in the second figure, married couples constituted the most dominant group in terms of adult marital status in both 1970 and 2000, though the corresponding percentage dropped from 70% to under 60%. People who never married contributed the second largest group in both years, which accounted for roughly 15% then 20% of the total population of adult Americans.