Tsuruoka City, Yamagata Pref. |
Random sampling |
"Panel research" |
(1) It is the world's longest-standing "real-time survey" on language change.
(2) It is a "trend survey" that has been implemented by conducting four questionnaire surveys
using basically the same questions on about 400 informants sampled randomly each time, at intervals of around
twenty years.
(3) It also contains data from "panel research", in which trend survey respondents were tracked
longitudinally, at about twenty-year intervals, using basically the same questions.