  In common law, the outcome of a new case is determined mostly by precedent
cases, rather than by existing statutes. However, how exactly does the
precedent influence the outcome of a new case? Answering this question is
crucial for guaranteeing fair and consistent judicial decision-making. We are
the first to approach this question computationally by comparing two
longstanding jurisprudential views; Halsbury's, who believes that the arguments
of the precedent are the main determinant of the outcome, and Goodhart's, who
believes that what matters most is the precedent's facts. We base our study on
the corpus of legal cases from the European Court of Human Rights (ECtHR),
which allows us to access not only the case itself, but also cases cited in the
judges' arguments (i.e. the precedent cases). Taking an information-theoretic
view, and modelling the question as a case outcome classification task, we find
that the precedent's arguments share 0.38 nats of information with the case's
outcome, whereas precedent's facts only share 0.18 nats of information (i.e.,
58% less); suggesting Halsbury's view may be more accurate in this specific
court. We found however in a qualitative analysis that there are specific
statues where Goodhart's view dominates, and present some evidence these are
the ones where the legal concept at hand is less straightforward.
