Technique 2.87 Logic Or Issue Trees (See Fan Concept)


These trees are used to visualise and disaggregate the challenges. They can be simple or sometimes highly complex.

Some types include hypothesis trees and decision trees. The power of these trees in problem-solving is based on
- providing a clear visual representation and understanding of the challenge and its components parts
- they are holistic in the sense that everything relevant is captured in the tree
- their format leads to clear hypotheses that can be tested with data and analysis

NB Need to keep in mind the risks around each component/element, ie what can go wrong? Can put a relative weight on each element or variable to reflect its importance in the final decision.

Types of Logic Trees


"...early on in the process we use the component of factor trees, and often work inductively (learning from specific cases that illuminate general principles later), to help us define basic problem structure. Later, after some iterations with data and analysis, we usually move to hypothesis tree, deductive logic trees or decision trees, depending on the nature of the problem..."
Charles Conn et al 2018

A Deductive Logic Tree.

It follows the process of logical deduction, ie sometimes expressed in quantities, typically logically or mathematically complete.

It is used when we know a lot about the logical structure of the problem.

Sometimes called "top-down reasoning" as we use it to move from general rules or principles to conclusions via more specific data and assertions, eg

General statement: all watchmakers need glasses

Specific observation: John wears glasses

Inductive conclusion: John is a watchmaker

NB Move from trees with general problem elements to trees that state clear hypothesis to test.
"...the goal in building logic trees is to find the levers that help us crack our problem, starting with the components that can help focus gathering and eventually moving towards the general hypothesis that can be tested. components of factors are just the most obvious elements that make up a problem......usually find enough information for a logical first disaggregation, with a small amount of Internet research and a team brainstorming session..."
Charles Conn et al 2018

Remember: vague labels do not drive analysis or action

An example of a Deductive Logic Tree



This tree shows us some of the secondary and tertiary levels of the problem, ie a good list of factors affecting the problem and possible areas of intervention. It provides a better direction for the next stage of research and relationship building around the problem. However, because it lacks any strong indication of the importance or magnitude of any factor. Thus it has limited use to develop a hypothesis to guide our data gathering, analysis and prioritisation.

Inductive Logic Trees

This process is the reverse of the deductive logic trees.

Inductive reasoning moves from a specific observation toward general principles, eg

Observations: watchmakers in a shop wear glasses

Inductive assertion: all watchmakers wear glasses

Inductive reasoning shows probabilistic relationships, not causal ones.
(sources: Charles Conn et al 2018)

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