SC QUALITY GUILDMatrix diagram (L-shaped and T-shaped)
SCQUALITYGUILD.COM/TOOLS/MATRIX-DIAGRAM.HTML
Put one list across the top and one or two down the side, and mark how strongly each pair is related. The tool totals each row and column and flags the rows and columns with no relationship at all.
ON THE EXAM · CQPA II.D.1, CQE V.B.4, CSSBB IV.D.3 · FREE · NOTHING YOU TYPE LEAVES YOUR BROWSER
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What a matrix diagram is for
A matrix diagram shows the relationships between the items of two or more lists. Each cell where a row and a column meet holds a symbol for how strongly they are related, or nothing. It is one of the seven management and planning tools and is used to answer questions such as: which actions address which complaints, which processes affect which requirements, or who is responsible for which task.
The shapes
- L-shaped: two lists, one down the side and one across the top. The most common.
- T-shaped: three lists. One list (across the middle) is related to two others, one above and one below. For example, actions related to complaints and to the departments that must carry them out. This tool draws the two row lists one under the other, sharing the columns.
- Y-shaped, X-shaped and C-shaped relate three or four lists in a circle or in three dimensions. They are rare in practice; the same relationships can be built from several L matrices.
Symbols and totals
The usual symbols are a double circle (◎) for a strong relationship, a circle (○) for medium and a triangle (△) for weak, scored 9, 3 and 1. The wide 9-3-1 spread makes strong relationships dominate the totals. Adding the scores across a row shows how well that row item is covered; adding down a column shows how much each column item matters across all the rows.
Reading the matrix
- An empty row is a gap: nothing in the other list addresses it. In a complaints-to-actions matrix, it is a complaint nobody is working on.
- An empty column is an item that serves nothing. Ask why it is there.
- A row with only weak links is covered on paper but not in fact.
- A column with a high total is a key item: it relates strongly to many rows.
- A matrix where nearly every cell is marked is not discriminating. Keep only relationships you could defend.
Matrix, prioritization matrix or house of quality?
A matrix diagram shows relationships. A prioritization matrix adds weights to the criteria and scores options to rank them. The house of quality is an L matrix of customer requirements against technical characteristics, weighted by customer importance, with a roof showing how the characteristics interact.
On the exam
Matrix diagrams are listed among the quality management tools in CQPA (II.D.1), the quality management and planning tools in CQE (V.B.4), and the analytical tools in CSSBB (IV.D.3). Expect to name the shapes (L, T, Y, X), to know the strong, medium and weak symbols and the 9-3-1 scoring, and to total a row or column.