Systematic investing

Systematic investing applies a defined, repeatable set of rules to investment decisions rather than relying on discretionary judgment at each decision point.

The rules are set in advance

The defining characteristic is that the decision is made before the situation arises. What gets held, when it changes, and what triggers the change are all specified ahead of time.

What it buys

Consistency, and a record. Every decision has a documented reason that existed before the decision, which is a materially different thing to explain to a client or a regulator than a judgment call made in the moment.

It also removes the specific failure where a process quietly changes under stress without anyone acknowledging it did.

What it costs

Rules cannot respond to circumstances they did not anticipate. A systematic process will do the wrong thing in a novel situation, confidently, because that is what following rules means.

Anyone selling systematic investing without saying that is selling something else.

The overfitting problem

Rules derived by searching historical data for what would have worked will always look excellent on that data. Whether they describe anything durable is a different question, and it is the central methodological risk in the whole approach.

A rule that has never been wrong has usually not been tested. It has been fitted.