Lean Sigma: A Practitioners Guide

13. Customer Requirements Tree

Overview

A Customer Requirements Tree is the last in a series of tools used to capture the VOC. The output of any Customer Interviews, along with output from Customer Surveys, are affinitized and then translated into a Customer Requirements Tree to identify the Big Ys or KPOVs for the process.

The tool is used to graphically show the major Customer Needs and associated metrics for the process, so that the Belt, Champion, and Process Owner can agree on the major metrics that the project will address.

An example Customer Requirements Tree is shown in Figure 7.13.1.

Figure 7.13.1. Example Customer Requirements Tree for an invoicing process.[23]

[23] Adapted from SBTI's Transactional Process Improvement Methodology training material.

The tree helps translates broad Customer requirements into specific critical requirements and then to detailed specifications.

Logistics

It speeds up completion of the Tree if the Belt does some draft construction prior to a working session with the Team. The primary input to the Tree is the Customer Requirements Affinity Diagram, so this needs to be readily accessible during construction.

A working session to construct the Tree in the Define Phase typically takes 12 hours, but often requires follow up on specific elements, which could theoretically go on well into Measure if no usable metrics exist or little is known about them. Signoff for Define, however, cannot be done until the Tree is complete and the subsequent KPOVs are defined.

Roadmap

The roadmap to constructing the Customer Requirements Tree starts much earlier, with the outputs from interviews and surveys being organized logically in an Affinity Diagram as shown graphically in Figure 7.13.2.

Figure 7.13.2. Construction of a Customer Requirements Tree.

Step 1.

Convert the Customer Requirements Affinity Diagram into a tree structure:

  • The highest level Categories in the Affinity become the Drivers (major branches)

  • The individual Voices or Needs become the Requirements

An example of a completed version of this is shown in Figure 7.13.3.

Figure 7.13.3. Initial Tree Structure from Affinity Diagram.

If the Affinity has more than one layer of grouping (the Team grouped the groups), then the tree has the following structure:

  • Drivers (major branches)

  • Sub-Drivers (sub-branches)

  • Requirements

Step 2.

For each requirement, identify the appropriate metric or metrics. Later, if the metric is deemed to be one of the KPOVs or Big Ys for the project, then some Measurement Systems Analysis (MSA) work is required to verify the reliability of the metric and specifically the ability to measure it.

Step 3.

For each metric list the specifications if they are known. The specifications can be determined only by the Customer, or from interaction with the Customer. Specifications might be known for a few metrics, but commonly are not known and some additional investigative work is required.

Interpreting the Output

The Customer Requirements Tree is used to identify the superset of major metrics for the process in question. Only a subset of these metrics can be efficiently tackled in a Lean Sigma process, so the Tree (in context of all the Customer Interviews and Customer Surveys) is used to guide the Belt and Champion in a discussion about what the selected target metrics should be for the project.

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