Introduction to Measurement

According to Lord Kelvin “When you can measure what you are speaking about and express it in numbers, you know something about it; but when you cannot measure, when you cannot express it in numbers, your knowledge is of a meager and unsatisfactory kind; it may be the beginning of knowledge, but you have scarcely, in your thoughts, advanced to the stage of a science.”

What is Measurement?  Measurement is the process by which numbers or symbols are assigned to attributes of entities in the real world in such way as to describe them according to clearly defined rules.

Why do we Measure?  To characterize

Why do we Measure?  To characterize  To evaluate

Why do we Measure?  To characterize  To evaluate  To predict

Why do we Measure?  To characterize  To evaluate  To predict  To improve

Some Difficult Measurement Questions  In a room with blue walls, is “blue” a measure of the color of the room?  Can intelligence be measured? Is IQ an adequate measure?  Should we reject measures because they cannot be accurately measured or because they depend on the judgment of the person doing the measuring?

Some Difficult Measurement Questions (Cont’d)  How do we decide which error margins are acceptable in measurement and which are not?  How do we determine the correct scale for a given measurement?  What kinds of manipulation are we able to do to our measurements and still have meaningful results?

Galileo Galilei (1564 – 1642) “What is not measurable make measurable”

Direct and Indirect Measures  Direct Measures – direct quantification as in measuring the height of a person.  Indirect Measure – calculations involving multiple measures as in a grade point average.

Measurement in Software Engineering  Computer Science provides the theoretical foundations for building software.  Engineering focuses on implementing the software in a controlled and scientific way.

Neglect of Measurement in Software Engineering  Failure to set measurable targets for our software products. (“Projects without clear goals will not achieve their goals clearly,” Tom Gilb)  Failure to understand and quantify the component costs of software projects.  Failure to quantify or predict the quality of produced products.  Guided by anecdotal evidence in deciding to try new approaches instead of doing carefully controlled studies

Tom DeMarco (1982) “You cannot control what you cannot measure”

Objectives for Software Measurement (Managers)  What does each process cost?  How productive is the staff?  How good is the code being developed?  Will the user be satisfied with the product?  How can we improve?

Objectives for Software Measurement (Engineers)  Are the requirements testable?  Have we found all the faults?  Have we met our product or process goals?  What will happen in the future?

Purposes of Measurement in Software Engineering  Understand  Control  Improve

The Scope of Software Metrics  Cost and effort estimation  Productivity measures and models  Data collection  Quality models and measures  Reliability models  Performance evaluation and models  Structural and complexity metrics  Capability maturity assessment  Management by metrics  Evaluation of methods and tools

Productivity Measures and Models

Quality Models and Measures