The early 20th-century accent of the Inland North was the basis for the term "General American", though the regional accent has since altered, due to the Northern Cities Vowel Shift: its now-defining chain shift of vowels that began in the 1930s or possibly earlier. A 1969 study first formally showed lower-middle-class women leading the regional population in the first two stages (raising of the vowel and fronting of the vowel) of this shift, documented since the 1970s as comprising five distinct stages. Evidence in the mid-2010s has suggested a reversal of some features of the Northern Cities Shift in certain locations.