Constructive Cost Model: COCOMO for Software Estimation
PMBOK v8 Definition
A constructive cost model (COCOMO) is a cost-estimation model for effort, time, and cost, usually associated with software development projects. The source lines of code or function points and adjustment factors are usually used as inputs and help to predict the software development cost.
This concept is part of the Project Cost Management knowledge area, specifically within the Estimate Costs process.
Why It Matters for the Exam
The PMI exam frequently tests COCOMO as a specialized parametric estimation technique used in software development projects. Questions often appear in the Estimate Costs process section, testing your ability to distinguish COCOMO from other estimation methods (analogous, parametric, bottom-up, three-point). Expect 1-2 questions that ask you to identify what type of model COCOMO is or what inputs it requires.
Key Points to Remember (for the exam)
- Type of Model: Parametric cost-estimation model (not analogous, not bottom-up)
- Primary Application: Software development projects specifically
- Main Inputs: Source lines of code (SLOC) or function points
- Adjustment Factors: Multiple separate adjustment factors are used as additional inputs
- Outputs Predicted: Effort, time, and cost for the software project
- Common Confusion: COCOMO is often mistaken for analogous estimation, but it is a parametric model using mathematical formulas with adjustment factors
- Key Distinction: Unlike simple parametric models (e.g., cost per square foot), COCOMO uses multiple separate adjustment factors, each with numerous points within it
Typical PMI Exam Example
Situation: A project manager is estimating costs for a new software development project. The team has historical data from similar projects and wants to use a model that incorporates source lines of code and multiple adjustment factors to predict effort and cost.
Question: Which cost-estimation technique is the project manager applying?
Correct Answer: Constructive cost model (COCOMO), because it is a parametric model designed specifically for software development using source lines of code and adjustment factors.
PMI Exam Traps
-
Trap: Confusing COCOMO with analogous estimation Reality: COCOMO is a parametric model using mathematical formulas and adjustment factors, not a simple comparison to past projects
-
Trap: Thinking COCOMO applies to all project types Reality: COCOMO is usually associated with software development projects specifically
-
Trap: Assuming COCOMO uses only one input variable Reality: COCOMO uses source lines of code or function points plus multiple separate adjustment factors, each with numerous points
-
Trap: Confusing COCOMO with bottom-up estimating Reality: COCOMO is a top-down parametric model, not a detailed bottom-up aggregation of individual activities
Important PMI Connections
| Related Concept | Relationship Type | Exam Attention Point |
|---|---|---|
| Parametric Estimation | Type of model | COCOMO is a specific parametric model; parametric uses mathematical models with project parameters |
| Historical Information Review | Input source | Historical information helps develop parametric models like COCOMO |
| Cost Estimates | Output | COCOMO produces cost estimates as a quantitative assessment of likely costs |
| Analogous Estimates | Different method | Unlike analogous (top-down using past projects), COCOMO uses mathematical formulas with adjustment factors |
Quick Review Questions
-
What type of cost-estimation model is the constructive cost model (COCOMO)?
-
Which two types of inputs are typically used in a COCOMO estimation?
-
For what type of project is COCOMO usually associated?
-
How does COCOMO differ from a simple parametric model like cost per square foot?
-
What three project aspects does COCOMO predict (effort, time, and what)?
PMBOK v8 Reference
Section 5.2 - Estimate Costs (Process Group: Planning, Knowledge Area: Project Cost Management)
Note: The COCOMO definition appears in the PMBOK v8 glossary and is referenced in the context of cost estimation techniques within the Estimate Costs process.