Decision tree maker

Drawn properly, it stops the same judgement call being made differently by different people on different days.

When a decision tree helps

• Support and returns policies, so the answer does not depend on who picks up
• Triage: what to escalate, and to whom
• Explaining eligibility rules to people who have to apply them
• Thinking through a choice with several conditions

Building the tree

1. Open the template and put your first question in the top diamond.
2. Label every branch leaving a question with the answer that takes you down it.
3. Keep going until every path ends in a rounded outcome shape, not a question.
4. Colour the outcomes: green for the easy yes, red for the firm no.
5. Walk three real cases through it and see whether they land where they should.
6. Export a PNG and put it where the decision gets made.

Keeping a tree usable

Every branch is labelled

An unlabelled line out of a diamond is the single most common mistake, and it makes the tree unusable.

Questions have answers, not opinions

“Is the order under 30 days old?” works. “Is the customer reasonable?” does not.

Every path ends

A path that stops at a question is a gap somebody will fall through.

Put the common case first

Order the questions so most cases reach an outcome in two or three steps.

A worked example: whether to repair or replace

Start with the decision at the root: Repair or replace the laptop? The first question is the one that rules out most options: Is it under warranty? Yes ends in a leaf, Send it for repair. No leads to a second question: Does the repair cost more than half the price of a new one?

Yes ends in Replace it. No leads to one last question, Is it more than five years old?, whose answers end in Replace it and Repair it. Three questions, four leaves, and every path ends in an action. The rule of thumb this shows is to put first the question that settles the most cases.

Decision tree questions