Introduction to Measurement

1
Introduction to Measurement
2
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.

3
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.

4
Why do we Measure?

• To characterize

5
Why do we Measure?

• To characterize
• To evaluate

6
Why do we Measure?

• To characterize
• To evaluate
• To predict

7
Why do we Measure?

• To characterize
• To evaluate
• To predict
• To improve

8
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?

9
Some Difficult Measurement Questions (Contd)

• 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?

10
Galileo Galilei (1564 1642)

• What is not measurable
• make measurable

11
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.

12
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.

13
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

14
Tom DeMarco (1982)

• You cannot control what you cannot measure

15
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?

16
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?

17
Purposes of Measurement in Software Engineering

• Understand
• Control
• Improve

18
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

19
Productivity Measures and Models
20
Quality Models and Measures