Most of Dr. Twenge's research focuses on the differences among generations (the academic term is birth cohort). The best way to find generational differences is to find data that’s been collected throughout time. Unlike a one-time survey, data over time can determine that differences are due to generation or time and not to age.
Twenge's students and she often conduct these studies using a variation on meta-analysis, finding journal articles and dissertations that gave people psychological scales over a period of several decades. She calls this cross-temporal meta-analysis (for more on this method, click here.
Large databases such as Monitoring the Future (of high school students) and the American Freshman (of entering college students) are also very useful for discovering generational differences. Between her own meta-analyses and these two databases, Twenge's generational studies draw from the responses of 11 million young people between the 1930s and the present. She has also drawn on other databases such as the Social Security Administration’s catalog of the names given to 325 million Americans since 1880. These studies have found generational differences in work attitudes, personality traits, attitudes, and behaviors.
She also does lab research on several topics, including social rejection and the influence of modern culture on personality traits.
For a list of some of Dr. Twenge's research articles, click here.