The document discusses the top 10 factors that have been proven to affect software reliability based on analysis of data from over 150 software projects. The top factors are: 1) Avoiding large code releases and teams to reduce complexity; 2) Mandatory developer testing; 3) Techniques that improve requirements and design visualization; 4) Identifying and testing unexpected behavior; 5) Involving domain experts; 6) Following full development processes; 7) Defect reduction techniques; 8) Tailored process improvement; 9) Configuration and change management; 10) Improved testing techniques rather than longer testing. The analysis is based on benchmarking over 500 development factors against actual defect data from various projects.

1. THETOPTENTHINGSTHAT HAVE BEEN
PROVENTO EFFECT SOFTWARE
RELIABILITY
Softrel, LLC
20 Towne Drive #130
http://www.softrel.com
amneufelder@softrel.com
Copyright © SoftRel, LLC 2011. This presentation may not be copied in
part or in whole without written permission from Ann Marie Neufelder.

2. About Ann Marie Neufelder
 Chairperson of the IEEE 1633 Recommended Practices for Software Reliability
 Since 1983 has been a software engineer or manager for DoD and commercial
software applications
 Co-Authored first DoD Guidebook on software reliability
 Developed NASAs webinar on Software FMEA and FTA
 Has trained every NASA center and every major defense contractor on software
reliability
 Has patent pending for model to predict software defect density
 Has conducted software reliability predictions for numerous military and
commercial vehicles and aircraft, space systems, medical devices and equipment,
semiconductors, commercial electronics.
Copyright © SoftRel, LLC 2011. This presentation may not be copied in
part or in whole without written permission from Ann Marie Neufelder. 2

3. There are 3 basic things that determine the
software MTTF and MTTCF
 This presentation will focus on the defect and defect density reduction
of defects that escape development and testing
Copyright © SoftRel, LLC 2011. This presentation may not be copied in part or in whole without written permission from Ann Marie Neufelder.
Factor Sensitivity Comments
Fielded defect
density/defects
Cutting this in half ->
doubles MTBF.
Reducing defects requires elimination of
development practices that aren’t effective as
well as embracing those that are
Effective code
size
Cutting effective size
in half -> doubles
MTBF.
• COTS and reuse can have big impact
• Error in size prediction has direct impact on
error in reliability prediction
Reliability
growth– how many
hours real end user
operate tank per
month after
deployment
Non-linear
relationship.
More of this after delivery means MTTF at end
of growth period is better but MTTF upon
delivery is less because more defects are found
earlier.

4. If you ask a software engineer to rank the top 10 factors
associated with unreliable software – this is what they
might say…
Copyright © SoftRel, LLC 2011. This presentation may not be copied in part or in whole without written permission from Ann Marie Neufelder.
Ranking Factors Where this factor actually ranks
1 Not enough calendar time to finish 457 - because usually late projects are late because
they started late and not because of insufficient
time
2 Too much noise 352
3 Insufficient design tools 126
4 Agile development So far, not a single project in our DB used this
completely and consistently from start to finish.
5 Existing code is too difficult to change 146
6 Number of years of experience with a
particular language
400 –What matters is the industry experience
7 Our software is inherently more difficult
to develop
370 – Everyone thinks this
8 Everybody has poor coding style 423 –While code with good style may be less error
prone, that doesn’t mean its defect free
9 Object oriented design and code 395 –While OO code may be more cohesive, that
doesn’t mean its defect free
10 If they would just leave me alone I could
write great code
Our data shows that the reverse is true

5. If you ask a software process engineer to rank the top 10 factors
associated with unreliable software – this is what they might say…
Copyright © SoftRel, LLC 2011. This presentation may not be copied in part or in whole without written permission from Ann Marie Neufelder.
Ranking Factors Where this factor actually ranks
1 Capability Maturity 417 - Organizations with low CMM can and have developed reliable
software. Defect density reduction in our DB plateaued at level 3.
2 Process improvement
activities
8 –The right activities tailored to the process can avoid a failed project
but not necessarily result in a successful project
3 Metrics 54 – Not all metrics are relevant for reducing defects. Too many metrics
or poorly timed metrics won’t reduce defects either.
4 Code reviews 366 - Because the criteria for the reviews is often missing or not relevant
to reducing defects
5 Independent SQA
audits
359 – Probability because the audits focus on product and often miss
technique
6 Popular metrics such as
complexity
430 – Fastest way tor reduce complexity is to reduce exception handling
which is necessary for reliability.
7 Peer reviews #368 - Because peer reviews are often lacking a clear agenda and
because peers don’t necessarily understand the requirements
8 Traceability of
requirements
61 –The problem is what’s NOT in the requirements. Requirements
almost never discuss negative or unexpected behavior.
9 Independent test
organization
295 – Organizations with this are less motivated to do developer testing
10 High ratio of testers to
software engineers
380 –Those that have this are often not doing developer testing

6. This is the top 10 list based on hard facts and data
1. Avoid Big Blobs – “Code a little –Test a little”. Avoid big and long releases, avoid big teams
working on same code, avoid reinvention of the wheel. Planning ahead and with daily or weekly
detail. Micromanage the development progress.
2. Mandatory developer white box testing at module, class and integration level
3. Techniques that make it easier to visualize the requirements, design, code, test or defects
4. Identifying, designing, coding and testing what the software should NOT do
5. Understand the end user. Employ software engineers with DOMAIN experience. Involve
customers in requirements, Prototyping, etc.
6. Not skipping requirements, design, unit test, test, change control, etc. even for small releases.
7. Defect reduction techniques – Formal product reviews, SFMEAs, root cause analysis.
8. Process improvement activities – tailored to the needs of the project
9. Maintaining version and source control, defect tracking, prioritizing changes. Avoiding
undocumented changes to requirements, design or code. Verifying changes to code don’t have
an unexpected impact.
10. Techniques for how to test the software better instead of longer
Copyright © SoftRel, LLC 2011. This presentation may not be copied in part or in whole without written permission from Ann Marie Neufelder.

7. How the “TopTen” list was developed
• Since 1993 Ann Marie Neufelder has benchmarked 679 development factors versus actual
defect data
• 156 factors were either employed by everyone or employed by no one in the database.
• The benchmarking was conducted on the remaining 523 factors.
• 75 complete sets and 74 incomplete sets of actual fielded defect data
• See backup slides for a summary of the projects in this database
• Benchmarking results yielded
• Ranked list of each factor by sensitivity to fielded defect density
• A model to predict defect density before the code is even written
• Refer to white paper “The Cold HardTruth about Reliable Software, Revision 6i”
Copyright © SoftRel, LLC 2011. This presentation may not be copied in part or in whole without written permission from Ann Marie Neufelder.

8. These are the actual fielded defect densities
for each of the projects in the database.
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0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
0 10 20 30 40 50 60
Actual
deployed
defect
density
per
EKSLOC
Project # in our DB
Actual fielded defect density of each project in database
If you can predict where
your software release is
with respect to those in
our database, you can
predict the reliability
These
software
projects were
distressed
These
software
projects were
successful

9. The 523 factors and the 4 P’s and aT
Factor
category
Number of
factors in this
category
Examples of factors in this category
Product 50 Size, complexity, OO design, whether the
requirements are consistent, code that is old and
fragile, etc.
Product risks 12 Risks imposed by end users, government
regulations, customers, product maturity, etc.
People 38 Turnover, geographical location, amount of noise
in work area, number of years of experience in
the applicable industry, number of software
people, ratio of software developers to testers,
etc.
Process 121 Procedures, compliance, exit criteria, standards,
etc.
Technique 302 The specific methods, approaches and tools that
are used to develop the software. Example:
Using a SFMEA to help identify the exceptions
that should be designed and coded.
Copyright © SoftRel, LLC 2011. This presentation may not be copied in part or in whole without written permission from Ann Marie Neufelder.
Now let’s see which development activities have been covered.

10. The 523 factors by development phases/activities
Activity associated with factor #Factors
Scheduling and personnel assignments 32
Project execution – making sure that work gets done on time and with desired
functionality
24
Software development planning 10
Requirements analysis 42
Architectural design 3
Design 32
Detailed design 22
Firmware design* 1
Graphical User Interface design* 2
Database design* 1
Network design* 1
Implementation – coding 54
Corrective action – correcting defects 11
Configuration Management (CM), source and version control 27
Unit testing – testing from a developers perspective 48
Systems testing – testing from a black box perspective 75
Regression testing – retesting after some changes have been made to the
baseline
4
Defect tracking 17
Process improvement 24
Reliability engineering 18
Software Quality Assurance 25
No activity – these are related to operational profile and inherent risks 33
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11. The factors associated with increased
defect density
1. Using short term contractors to write code that requires
domain expertise and is sensitive to your company
2. Reinventing the wheel – failing to buy off the shelf when
you can
3. Large projects spanning over many years with many
people
4. “Throw over the wall” or “Big Blob” testing approach
which is very common in industry
Copyright © SoftRel, LLC 2011. This presentation may not be copied in part or in whole without written permission from Ann Marie
Neufelder.
Now that we’ve seen what causes high defect density, let’s see what causes a failed
project…

12. All failed projects had these things
in common
•They started the project late
•They had more than 3 things that required a learning
curve
• New system/target hardware
• New tools or environment
• New processes
• New product (version 1)
• New software people
•They failed to mitigate known risks early in the project
Copyright © SoftRel, LLC 2011. This presentation may not be copied in part or in whole without written permission from Ann Marie Neufelder.
What’s not on these lists is as important as what
IS on these lists….

13. The factors that didn’t correlate one way or the
other to reduced defect density
• Overhyped software metrics such as complexity, depth of nesting, etc.
• Interruptions to software engineers (some interruptions are good while
others are not)
• Having more than 40% of staff doing testing full time (usually indicates
poor developer testing)
• CMMi levels > 3
• Coding standards that don’t have criteria that are actually related to
defects
• Metrics that aren’t useful for either progress reporting, scheduling or
defect removal
• Peer walkthrus (when the peers don’t have domain or industry experience)
• Superficial test cases
• Number of years of experience with a particular language
Copyright © SoftRel, LLC 2011. This presentation may not be copied in part or in whole without written permission from Ann Marie Neufelder.

14. Conclusions
• The benchmarking results were used to identify the factors that result in
fewer or more defects
• The ranked list was used to develop a model to predict defect density
before the code is written
• This model is available in
• The Software Reliability Toolkit
• The Software Reliability ToolkitTraining Class
• The Frestimate software
• The Software Reliability Assessment services
• Traditional software reliability models are used late in testing when there
is little opportunity to improve the software without delaying the
schedule
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15. BACKUP SLIDES
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16. Software reliability defined
• Probability of success of the software over some specified mission time
• Term commonly used to describe an entire collection of software metrics.
• Also defined as a function of
• Inherent defects
• Introduced during requirements translation, design, code, corrective
action, integration, and interface definition with other software and
hardware
• Operational profile
• Duty cycle
• Spectrum of end users
• Number of install sites/end users
• Product maturity
Copyright © SoftRel, LLC 2011. This presentation may not be copied in part or in whole without written permission from Ann Marie Neufelder.
These things
can be
predicted
before the
code is written

17. RelatedTerms
• Error
• Related to human mistakes made while developing the software
• Ex: Human forgets that b may approach 0 in algorithm c = a/b
• Fault or defect
• Related to the design or code
• Ex:This code is implemented without exception handling “c = a/b;”
• Defect rate is from developer’s perspective
• Defects measured/predicted during testing or operation
• Defect density = defects/normalized size
• Failure
• An event
• Ex: During execution the conditions are so that the value of b approaches 0 and the
software crashes or hangs
• Failure rate is from system or end user’s perspective
• KSLOC
• 1000 source lines of code – common measure of software size
Copyright © SoftRel, LLC 2011. This presentation may not be copied in part or in whole without written permission from Ann Marie Neufelder.

18. Who’s doing software reliability predictions?
 Space systems
 Missiles defense systems
 Naval craft
 Commercial ground vehicles
 Military ground vehicles
 Inertial Navigation and GPS
 Command and Control and Communication
 ElectronicWarfare
 General aviation
 Medical devices
 Healthcare/EMR software
 Major appliances
 Commercial electronics
 Semiconductor fabrication equipment
 HVAC
 Energy
Copyright © SoftRel, LLC 2011. This presentation may not be copied in part or in whole without written permission from Ann Marie Neufelder.
18

19. About the projects in this database…
Copyright © SoftRel, LLC 2011. This presentation may not be copied in part or in whole without written permission from Ann Marie Neufelder.
29%
5%
7%
10%
1%
5%
5%
38%
Defense
Space
Medical
Commercial electronics
Commercial transportation
Commercial software
Energy
Semiconductor fabrication

20. The benchmarking revealed 7 percentile groups in
which the project defect densities are clustered
Copyright © SoftRel, LLC 2011. This presentation may not be copied in part or in whole without written permission from Ann Marie Neufelder.
20
•Percentile group predictions…
•Pertain to a specific product release
•Based on the number of risks and strengths
•Can only change if or when risks or strengths change
•Some risks/strengths are temporary; others can’t be changed at all
•Can transition in the wrong direction on same product if
•New risks/obstacles added
•Strengths are abandoned
•World class does not mean defect free. It simply means better than
the defect density ranges in database.
Fewer fielded defects
97%
Failed
10%
Very
good
75%
Fair
50%
Average
25%
Good
More risks than strengths More strengths than risks
Strengths and risks
Offset each other
More fielded defects
90%
Poor
3%
World
Class