I am confused about when and to what extent parity is violated in weak decays. On the one hand, there's Wu's famous experiment where electrons are emitted preferentially in one direction. This parity violation can be said to be maximal, since all electrons are emitted in one direction. However, at the same time when determining the angular momentum and spin state of the electron-neutrino system in nuclear β-decay, I do use parity conservation as parity is mostly conserved. Could anyone explain why parity is violated maximally in the case above and minimally in the other case? Also, to what extent (~0.1%, ~1%, etc of cases) is parity violated in nuclear β-decay?