self-selected
adjective uk/ˌself.sɪˈlek.tɪd/ us/ˌself.səˈlek.t̬ɪd/ (also self-selecting, /ˌself.sɪˈlek.tɪŋ/ /ˌself.sɪˈlek.tɪŋ/)
自我选拔的
involving people or organizations that choose to take part in an activity, rather than being chosen by someone else
a self-selected sample of boys 一群自我选拔的男孩样本