Useful Statistics about Maintainability

Here are some useful statistics collected from several papers:

Concise and Consistent Naming:

• Approximately, 70% of software programs are identifiers. Therefore, identifiers names are of paramount importance for readability

Unused Features: From this paper:

• Jim Johnson (the Standish Group) in his keynote at XP2012 reports that 45% of the features in the analyzed systems were never used
• Industrial business information system showed that 28% of its features were never used
• 25% of all method genealogies were never used

Code Clones and defects: Some very useful statistics from this paper: Do code clones matter?:

• 52% of code clones are inconsistent
• of these inconsistencies, 28% are introduced unintentionally, and 18% are faults in the system
• Overall, 10% of code clones are defective

Architectural documentation & decay:

• 9%-19% conformance of implementation to architecture, 72%-90% of these non-conformances are due to flaws in documentation
• 10%-28% decay in architecture

How much clones cost?

• 20% effort increase in maintenance due to code clones