Protocol
Use a decision tree when sequence changes what you know
Order matters when tomorrow's decision gets to learn from today's outcome.
When it fits
- A choice can be followed by new information and later choices depend on what happened earlier.
When to avoid it
- Large trees grow exponentially; collapse irrelevant branches or use an influence diagram when the tree stops aiding understanding.
Why it matters
Draw branches in the order decisions and uncertain events occur. At each decision node, include only the information that would actually be known then. Put consequences at the leaves. This makes staged commitments, options to wait, tests and contingent actions visible instead of averaging them into one static comparison.
Steps
- Place the first decision or uncertain event at the root.
- Branch only on distinctions that affect a later action or consequence.
- At later decision nodes, use only information available by that point.
- Attach outcome/value information to terminal paths.
- Prune branches that cannot change the decision or consequence.
An example
Choose whether to pilot a tool now, observe pilot results, then decide whether to scale rather than evaluating 'buy or not buy' as one irreversible decision.
Check your result
The model shows at least one place where waiting for information or staging commitment changes the available decision.
Keep this limit in mind
- Large trees grow exponentially; collapse irrelevant branches or use an influence diagram when the tree stops aiding understanding.
Evidence and sources
Decision trees branch over decisions and uncertain states in the order those distinctions become known, making sequence explicit.
Large trees become unwieldy; influence diagrams or simulation may be more practical for complex problems.
Fifty years of decision analysis in operational research: A review · Decision trees