Connected Concepts - Business Management Consulting Services

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How To Read A Cause – Effect Logic Diagram (Tree)

Cause – Effect diagrams are an important tool for communicating logical ideas. We express cause and effect relationships as follows:

You read the relationships starting at the bottom as "If customers are buying more of our competitor’s products then customers aren’t buying as many of our products" followed by the next relationship "If customers aren’t buying as many of our products then Sales have decreased". And so on up the chain or branch of relationships.

An important fact about "cause-effect" relationships is that most effects have multiple causes. Sometimes causes are independent of each other. Sometimes they are dependent. Fig. 2 and Fig. 3 shows us some examples of independent and dependent causes.

Fig. 1 Intermediate levels of cause and effect

example 3.gif (5212 bytes)

Fig. 2 Independent causes (Logical OR)

We read the above diagram fragment as follows: "If the dogs dumped the trash can then trash litters the yard" or "If a strong wind blew the trash can over then trash litters the yard" or "If someone driving past our yard threw litter out of their car window then trash litters the yard". Each cause independently creates the effect. Eliminating any one of the causes does not eliminate the effect.

example 2.gif (5703 bytes)

Fig. 3 Dependent Causes. (Logical AND)

We read the above diagram fragment as follows: "If the room has uncovered windows and it is night time and the room lights are turned off then the room is dark". We also read: "If the room lights are turned off and the window shades are drawn closed then the room is dark."

We see that if any component of a logically dependent cause is removed then the cause is no longer logically valid. In this example we have two independent logically dependent causes, either of which results in the stated effect. Removing one logically dependent cause doesn’t eliminate the effect. But in this example we also see that the cause "the room lights are turned off" is a common component cause of both logically dependent causes and therefore if we remove this component cause neither logically dependent cause will be valid and the effect no longer will exist.

The Current Reality Tree

The Current Reality Tree is a logic tool that builds on the cause and effect relationships of entities and is used to identify one or more core problems that are responsible for the majority of an organization’s undesirable effects. It consists of undesirable effects (UDEs) which are related through cause-effect relationships in a tree structure until we determine the root causes that created these UDEs. One or two of the root causes will usually be responsible for the largest percentage of UDEs. These are referred to as the core problems. If we remove the core problems then we break the chains of valid logical cause and effect relationships that lead to the UDEs and we should see desirable effects take their place. The legend shown in Fig. 4 below is used in the Current Reality Tree. example 4.gif (12631 bytes)

Fig. 4 Current Reality Tree Entity Legend

NOTE: The three or four-digit diagram number for each entity indicates the page where the entity first appears in the logic tree. The first digit or the first two digits is the page number.

The Future Reality Tree

The Future Reality Tree is a logic tool that builds on the cause and effect of entities and is used to validate the impact of one or more injections (proposed solutions) into our current reality as previously described in the Current Reality Tree. The legend shown in Fig. 5 below is used in the Future Reality Tree. example 5.gif (12710 bytes)

Fig. 5 Future Reality Tree Entity Legend

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