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Economic turbulence and technological change in 2018 continued to roil major industry sectors, particularly in media, healthcare, and energy.

In our biennial Corporate Longevity report, Innosight tracks what economist Joseph Schumpter called “creative destruction” by using turnover in the S&P 500 index as a proxy for disruptive change. Our most recent projections, based on 2017 data, forecasts a steady decline in tenure over the next decade.

Checking in on S&P turnover in 2018, a total of 23 companies dropped out of the S&P 500 and were replaced by new ones. That makes four years in a row the number has been above 20 firms (28 in 2015 and 2016 and 26 in 2017).

The 2018 turnover rate is roughly in line with our forecast that the longevity rate of corporations in the S&P will nudge down slowly until 2020. We had forecast the 2018 rolling 7-year average tenure to be 21.4 years–and it came in at 22.3 years.

Among the year’s dropouts were some major acquisition targets such as Aetna, Monsanto, Time Warner, Express Scripts, and Scripps Interactive Networks.

Among the new S&P entrants replacing them were Twitter, WellCare, Abiomed, IPG Photonics, and Keysight Technologies.

Healthcare was one of the most active sectors, with five drop-outs and three additions. The Aetna-CVS merger as well as the Cigna acquisition of ExpressScripts are not just about consolidation but about leaping across prior business boundaries to forge a new customer-centric health experience.

In the energy space, four firms dropped out and four entered the index, as the sector continues to be among the most turbulent, due to the changing mix of fuel sources and the challenges posed by climate change.

In media, just two companies were removed from the index, but they were the result of ground-shifting deals. AT&T’s $100 billion buyout of Time Warner showcased the convergence of distribution and content, while Discovery’s $12 billion buyout of Scripps creates one of the largest content companies for both cable and digital distribution.

We expect transformational change in these and other industries to accelerate. Our longer-term forecast expects the longevity rate to plunge during the next decade—dropping down to a 12-year average lifespan by 2027.