Unlike obiter dicta, the ratio decidendi is, as a general rule, binding on courts of lower and later jurisdiction—through the doctrine of stare decisis.
The process of determining the ratio decidendi is a correctly thought analysis of what the court actually decided—essentially, based on the legal points about which the parties in the case actually fought.
As an example, the ratio in Donoghue v. Stevenson would be that a person owes a duty of care to those who he can reasonably foresee will be affected by his actions.
Factors that can either strengthen or weaken the strength of the holding include: The difficulty in the search for the ratio becomes acute when in the decisions of the Court of Appeal or the House of Lords, more than one judgment is promulgated.
However, one will sometimes find decisions in which, for example, five judges are sitting the House of Lords, all of whom purport to agree with one another but in each of whose opinions one is able to discern subtly different ratios.