Understanding Society User Support

Hello, I am interested in exploring the data of ethnicity in the Understanding Society report. I understand the questions of ethnicity/nationality are asked every 2 years in a wave. I wonder how often does the researcher asks people's nationality in a wave? Does the researcher ask once at the beginning of every wave, or they would ask a few times in a wave to observe the changes? I am also curious are the participants' pools different across the waves? Will it be the same group of people, or it is intended to interview different people in the community?