I'd add z-score (standard score) to your tool belt. The ability to identify or reject outliers is invaluable when trying to stabilize real-world business processes.
For example, if you are building heuristics that determine if a customer's bank account is "reasonably active", you may not want to consider very small transactions unless that is typical activity for a given customer.
For example, if you are building heuristics that determine if a customer's bank account is "reasonably active", you may not want to consider very small transactions unless that is typical activity for a given customer.