In the U.S., the Pew Research Center, a non-partisan think-tank, delineates a Generation X period of 1965–1980 which has, albeit gradually, come to gain acceptance in academic circles. Moreover, although fertility rates are preponderant in the definition of start and end dates, the center remarks: "Generations are analytical constructs, it takes time for popular and expert consensus to develop as to the precise boundaries that demarcate one generation from another." Pew takes into account other factors, notably the labor market as well as attitudinal and behavioral trends of a group. Writing for Pew's "Trend" magazine in 2018, psychologist Jean Twenge observed that the "birth year boundaries of Gen X are debated but settle somewhere around 1965–1980". According to this definition, the oldest Gen Xer is 55 years old and the youngest is, or is turning, 40 years old in 2020.