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What is a Matrix Diagram in PMP?

what is a matrix diagram in pmp

A matrix diagram is a visual tool used in project management that shows the relationship between two or more factors or variables. It is particularly useful for illustrating how various components of a project relate to and depend on each other.

In the Project Management Professional (PMP) exam, matrix diagrams frequently show up in questions related to the planning phase of a project. They help depict the logical relationships between activities, work packages, or other elements. Understanding how to interpret matrix diagrams is an important skill for PMP aspirants.

What is a Matrix Diagram in PMP?

Types of Matrix Diagrams

There are several types of matrix diagrams commonly seen on the PMP exam:

Activity-on-node (AON) diagram:

Activity on node Diagram

An AON diagram shows the sequence of activities in a project and the dependencies between those activities. In an AON diagram:

– Each activity is represented by a node (usually a box). The nodes are connected with arrows to depict dependencies.

– The arrows indicate the sequence and flow. An arrow points from the predecessor activity to the successor activity.

– Start and end nodes are distinct. The start node has no predecessors coming into it, while the end node has no successors going out.

– Different types of dependencies can be shown:
Finish-to-start (FS): A successor activity cannot start until its predecessor is finished.
Finish-to-finish (FF): A successor cannot finish until its predecessor finishes.
Start-to-start (SS): A successor cannot start until its predecessor has started.
Start-to-finish (SF): A successor cannot finish until its predecessor has started.

– The critical path is depicted by highlighting the sequence of activities that determine the shortest time to complete the project.

AON diagrams provide a clear visualization of the order of activities and how they logically relate to each other. They help optimize scheduling and resource planning. On the PMP exam, AON diagrams are useful to analyze the project timeline and critical path.

– Activity-on-arrow (AOA) diagram:

activity on arrow (AOA) diagram

In an AOA diagram:

  • Activities are represented by arrows between nodes rather than boxes.
  • The nodes denote events or milestones that mark the start and end of activities.
  • The arrows show the sequence of activities and the dependencies between them. An arrow points from the predecessor event to the successor event.
  • The start and end nodes indicate the initiation and completion of the project.
  • Like AON diagrams, AOA diagrams can depict finish-to-start, finish-to-finish, start-to-start, and start-to-finish dependencies.
  • The critical path is shown by highlighting the sequence of activities on the longest path to complete the project.
  • Dummy activities may be depicted as dotted arrows to show logical relationships between events where no actual work is performed.

AOA diagrams provide the same benefits as AON diagrams for visualizing activity sequencing and dependencies. The key difference is that activities are represented by arrows rather than boxes. On the PMP exam, the principles for analyzing AOA diagrams are identical to AON.

The choice between AON and AOA is largely stylistic, though some project managers prefer AOA since it emphasizes events rather than activities. Both diagram types are important to understand for the PMP exam.

– Responsibility assignment matrix (RAM): 

A RAM illustrates the roles and responsibilities of project team members across various work packages or activities. In a RAM:

  • Team members (or groups) are listed down the left vertical axis.
  • Work packages or activities are listed across the top horizontal axis. This creates a matrix.
  • At the intersection of a team member and work package is an indicator denoting their role:
    • Responsible (R) – Does the work
    • Accountable (A) – Final approver
    • Consulted (C) – Provides input
    • Informed (I) – Notified of outcomes
  • A RACI matrix is a specialized type of RAM that includes Responsible, Accountable, Consulted, and Informed designations.

Key benefits of a RAM/RACI include:

  • Clarifies roles and responsibilities for each activity.
  • Visualizes resource allocation and commitments.
  • Identifies gaps or overlaps in responsibility.
  • Reduces ambiguity and conflicts.
  • Facilitates coordination between team members.

On the PMP exam, a RAM question may ask you to interpret the allocation of work or identify missing roles based on the matrix. The RAM is an important technique for planning and managing resources.

– RACI matrix:


The RACI matrix is a type of responsibility assignment matrix that uses the following four designations:

Responsible (R) – The person or group actually performing the work. There is typically one role listed as Responsible per activity.

Accountable (A) – The person ultimately answerable for the correct and thorough completion of the work. There is only one Accountable specified per activity.

Consulted (C) – Individuals or groups who provide input, advice, and subject matter expertise. There may be multipleConsulted roles.

Informed (I) – Those kept up-to-date on progress and outcomes. There may be multiple Informed roles.

The RACI matrix provides a clear visualization of roles across activities:

raci matrix table diagram
img source: infodiagram

– Each team member is assigned only one of the RACI designations per activity.

– Many activities have just one Responsible, Accountable, and Consulted role.

– Most activities have multiple people Informed.

Benefits of the RACI include:

– Clarifies precisely who does what per activity.

– Eliminates confusion by assigning single-point accountability.

– Highlights gaps and overlaps in responsibility.

– Improves coordination through the inclusion of Consulted roles.

On the PMP exam, focus on grasping who is Responsible and accountable when analyzing a RACI matrix. This reveals who will do the work and who has decision authority.

How to Read Matrix Diagrams

When you encounter a matrix diagram on the PMP exam, look for these key components:

Nodes – Represent activities, work packages, events, etc. depending on the type of diagram.

Arrows/Lines – Denote relationships and dependencies between nodes. The direction of the arrows shows flow.

Legend – Provides definitions for any symbols used in the diagram.

Matrices – Visualize relationships between roles, activities, timelines, etc.

To correctly interpret a matrix diagram:

– Identify the start and end nodes. Understand the flow

Here are some tips on identifying the start and end nodes on a matrix diagram:

  • The start node is the point where the diagram begins. It will not have any predecessor activities or arrows coming into it.
  • The end node is the point where the diagram terminates. It will not have any successor activities or arrows going out of it.
  • Any nodes with arrows only coming into them and none going out are also end nodes for branches or paths within the diagram.
  • Similarly, nodes with only arrows going out and none coming in are start nodes for specific branches.
  • Follow the direction of the arrows between nodes to understand the flow and sequence. Arrows denote dependencies and the order of activities.
  • Activity or event names on the nodes can provide clues on what is starting and ending. Names like “Initiate project”, and “Complete testing” indicate start and end points.
  • For AON diagrams, look for unique start and end activity boxes. In AOA diagrams, look for start and end events.
  • On RAM and RACI matrices, there are no specific start and end points, but you can scan for the first and last rows/columns.

Identifying the start and end points provides critical context for correctly interpreting the relationship between activities and the overall flow of the project. This is an important first step in analyzing matrix diagrams on the PMP exam.

Note relationships between nodes based on connecting arrows

Here are some tips for noting the relationships between nodes based on connecting arrows in a matrix diagram:

  • Arrows indicate dependencies and the sequence of activities. An arrow connects two related nodes.
  • The direction of the arrow shows the flow and dependency. The node the arrow points from is the predecessor. The node the arrow points to is the successor.
  • On AON diagrams, make note of finish-to-start, finish-to-finish, start-to-start, and start-to-finish dependencies based on the connecting arrows.
  • On AOA diagrams, the arrows represent activities and connect the events/milestones they are dependent on.
  • Pay attention to parallel or converging arrows. This shows concurrent activities or dependency paths merging.
  • Diverging arrows represent a single node triggering multiple parallel activities.
  • Double-headed arrows indicate a two-way interdependency between nodes.
  • Dotted arrows often signify a lag or delay between connected nodes.
  • Loops back to a prior node demonstrate iterative or repeating activities.
  • No arrows between unconnected nodes imply no direct dependency relationship.

Clearly noting these node relationships revealed through the arrows allows you to accurately sequence activities, identify the critical path, and grasp interdependencies. This skill is essential for analyzing matrix diagrams on the PMP exam.

For matrices, read across rows and down columns to grasp relationships.

Here are some tips for reading across rows and down columns in a matrix diagram to understand relationships:

– In a RAM or RACI matrix, the rows represent team members or roles while the columns reflect activities or work packages.

– Read horizontally across each row to see all the responsibilities assigned to that role across different activities.

– Read vertically down each column to see all the roles assigned to that specific activity.

– Look for patterns:
– A team member assigned repeatedly to activities indicates breadth of responsibility.
– Many roles listed for a single activity denote shared collaboration.
– Sparsely populated columns mean fewer roles involved.
– Blank intersections may reveal gaps in responsibility.

– Identify outliers:
– Who is solely responsible role on critical tasks?
– Who has approval authority on key decisions?
– Who is informed on almost everything?

– Watch for overlaps:
– Are multiple people listed as Responsible for one activity?
– Is there ambiguity around Accountability?

Reading across and down provides a thorough understanding of resource allocation, gaps, bottlenecks, and patterns of responsibility. Practice this technique when reviewing matrices on the PMP exam.

Reference the legend to comprehend what each symbol means

Here are some tips on referencing the legend in a matrix diagram:

– Most matrix diagrams will have a legend or key explaining what the different symbols, colors, and icons represent.

– The legend is usually positioned on the side or bottom of the diagram.

– Typical legend elements include:

– Definitions for shapes used for nodes and arrows. Circles, squares, and arrows may have specific meanings.

– Colors for nodes and arrows that denote different types of activities or dependencies.

– Icons or abbreviations used within matrix boxes to assign roles and responsibilities.

– For RAM and RACI diagrams, the legend will provide the full meaning for R, A, C, I, and other abbreviations.

– On activity diagrams, the legend explains symbols used for milestones, delays, critical paths, etc.

– Pay close attention to the verbiage used in the legend definitions. The words provide clues to interpreting the symbols.

– If multiple formats are used on the diagram, ensure you check the legend to understand each one.

– Don’t make assumptions about what symbols mean without referring to the legend.

Using the legend effectively will help you accurately comprehend the full range of information conveyed in a matrix diagram. Make reading the legend a habit.

With some practice, you’ll be able to quickly decipher matrix diagrams on the PMP exam! They are an efficient way to represent logical connections and assignments between multiple moving parts of a project.

We hope you completely understand What is a Matrix Diagram in PMP with our detailed blog post.

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