Piau-chún phian-chha (標準偏差) tī ki-lu̍t thóng-kè tiong siōng chia̍p the̍h-lâi chò-ûi chhek-liông chi̍t-cho͘ sò͘-ta̍t ê lī-sàn thêng-tō͘ sú-iōng, Eng-gí kóng standard deviation (SD), sò͘-ha̍k hû-hō sī σ (sigma). Piau-chún phian-chha ê tēng-gī: