Wikipedia describes an Issue tree as a graphical breakdown of a question that dissects it into its different components vertically, and that progresses into details as it reads to the right.
Issue trees are useful in problem-solving to identify the root causes of a problem as well as to find potential solutions.
There are two types of issue trees: diagnostic and solution.
Diagnostic trees breakdown a “Why” key question, identifying all the possible causes for the problem. “Why” issue tree is more powerful tool than famous 5 Whys approach because it doesn’t isolate a single root cause but can consider several sources of the problem.
Solution tree breakdowns a “How” key question, identifying all the possible alternatives to fix the problem.
An issue tree needs following some basic rules:
- Progress from the key question to the analysis. (Chevallier., 2010)
– A tree goes from the key question to the data sources.
– Each tree follows the same pattern – either it is a “how” or a “why” but not both.
– “How” trees do not describe a sequential process but show alternative solutions.
– Items in the tree have to be clear questions, action verbs or hypotheses. Not just titles that have to be additionally clarified.
– Each move to the right must bring some value.
– Each item has at least 2 sub-items. If there is only 1 sub-item either there are other possibilities or some sub-items are redundant.
- Be ICE
– Independent and Collectively Exhaustive (ICE) means that all items are independent of each other and at least one of them must occur. “For example, when rolling a six-sided die, the outcomes 1, 2, 3, 4, 5, and 6 are Collectively Exhaustive, because they encompass the entire range of possible outcomes.”
Issue tree is Sequencing,
Evidencing, and Holistic.
– McKinsey recommends relying on Mutually Exclusive and Collectively Exhaustive groupings for an issue tree creation. However, in practice, Mutually Exclusive requirement is not efficient because of a combination of different approaches can give much better results than just one exclusive solution. So in the real life problem-solving ICE approach is mostly exploited. (Chevallier)