context: As of 2014, IPv4 still carried more than 99% of worldwide Internet traffic. The Internet exchange in Amsterdam and Seattle are the only large exchanges that publicly show IPv6 traffic statistics, which as of October 2018 are tracking at about 2.9% and 7.7%, growing at about 1.9% and -2.6% per year, respectively. , the percentage of users reaching Google services with IPv6 reached 25.0% for the first time, growing at about 4.2% per year. This growth is down from 7.2% per year between July 2016 and July 2017.  about 27% of Alexa Top 1000 web servers support IPv6.
question: How many years was growth down 7.2% in 2016 and 2017?
answer: 1