Bias 和 prejudice 都意為「成見，偏見」。就此意思而言，這兩個字並無太大差異，而兩者皆可用作可數和不可數名詞。此外，它們亦均可當及物動詞用。但無論是當名詞還是當動詞用，其後慣用的介詞或介詞片語都是 against 或 in favor of；若接 against，則意為「對….有偏見、成見」，若接 in favor of，則意為「偏愛，偏袒」。
Bias 是指基於個人好惡或成見而提出的偏差的意見或作出的偏心或偏袒的判斷，如 The boss was accused of bias towards employees over 50. (那個老闆被控對 50 歲以上的員工有偏見)；The art collector has a bias in favor of Monet. (這位藝術品收藏家偏愛莫內的畫作)；Professor Lee could not possibly be under any bias. (李教授不可能存有任何偏見)。
Prejudice 是指毫無根據的判斷或基於私人感情的成見或歧視，常帶有惡意，如 Bridget has a prejudice in their favor. (布麗姬對他們有所偏愛)；Mary’s father had a prejudice against her boyfriend. (瑪麗的父親對她的男友有偏見)；His remarks are prejudice against scholars in politics. (他的話是對學者從政的偏見)。
然而，prejudice 還有「歧視」的意思，而這是 bias 所沒有的，如 racial/sexual prejudice (種族/性別歧視)。所以，在下面兩句中，我們只能用 prejudice，不可用 bias：
- The government has taken measures to prevent racial prejudice against foreigners. (政府已採取措施來防止對外國人的種族歧視)
- The company was accused of having a sexual prejudice against his women employees. (那家公司被控對女員工性別歧視)