Complex sentence: The most serious negative social effect of this downturn has been the emergence of chronic unemployment; average unemployment rates during the 1980s were generally under 5%; by the mid- 1990s this level had risen to over 20%.
Split into simpler sentences: The most serious negative social effect of this downturn has been the emergence of chronic unemployment. Average unemployment rates during the 1980s were generally under 5%; by the mid- 1990s this level had risen to over 20%.