what does it cost to fix a defect

8/12/2019 What Does It Cost to Fix a Defect

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What Does It Cost to Fix a Defect?

ByJohanna Rothman

Summary: We all have different attitudes and policies toward finding and fixing defects. The choiceabout whether and when to fix defects depends upon many factors, one of the least understood being

the actual cost of fixing a defect. In this wee!s column, testing expert Johanna Rothman shares a

formula for calculating the system test cost to fix defects and how to factor that into the bigger picture

of your pro"ect.

#an is a developer woring on a pro"ect, along with four other people. They spent the first eight

months of the pro"ect developing the product without fixing their defects, unless the defect prevented

them from moving forward with development. #an and his team thought it would be more cost$

effective to fix their defects all at once. %o at month nine, about a month away from the desired

release date, they decided it was time to fix the defects.

&very is a pro"ect manager at a company with a virtual loc on the maret. Because the customers are

captive, each customer wants a beta copy immediately, so they can start using the software.

'oncerned that a beta with many defects would mae their customers angry, &very decided it would

be more cost$effective and less risy for the developers to find and fix the ma"ority of the defects

before they started system test.

Two pro"ects, two completely different approaches toward finding and fixing defects. We all have

different attitudes toward fixing defects, specifically which ones to fix and when. The choice to fix or not

to fix depends upon many factors( the ind of product you!re developing) the riss associated with

shipping nown or unnown defects) your development processes) and what it will cost you to fix the

defect when you dofix it.

*ne of the least understood factors is the actual cost of fixing a defect. This cost feeds bac into your

choice of development lifecycle and development process and can help you decide how much ris

you!re willing to tae to ship or not ship the product. +owever, many people don!t actually now what it

costs their organiations to fix a defect. If you!re not sure either, here is an estimation techni-ue to

measure that cost(

In system test, when people are // percent dedicated to finding and fixing defects, count the number

of fixes. 0ou now how many people 1developers, testers, and anyone else2 wored on the pro"ect,

and you now the duration of system test. This allows you to calculate the cost to fix a defect during

this phase of the pro"ect. +ere!s how you can find the average cost to find and fix a defect(

&verage cost to fix a defect 3 14umber of people 5 number of days25 cost per person$day14umber of fixed defects2
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&very / 89//


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days

8/?,>9/ 9 person$

days

8,>9/

&very has high system test costs, because his pro"ect spends more time looing for defects than fixing

defects +owever, &very!s total defect fix cost for &very!s larger pro"ect is lower than #an!s smaller

pro"ect. &nd &very!s post$release fix cost is substantially lower.

ach pro"ect will have its own cost to fix a defect, because the cost depends on the activities

undertaen in the pro"ect and when you start tracing defects, as well as cost to fix. :se your fix cost

to decide how you want to proceed with this pro"ect or the next one. If your cost is too high, and you!re

not yet in system test, you could try some defect detection and prevention techni-ues. Just mae surethat if everyone is associated with finding and fixing defects that you don!t only count the fix time, that

you count the detection time also.

If your find$and$fix cost is high in system test, what!s the ris of releasing earlyC &very might have

used his find$and$fix cost of 8???? to chose to end system test early and release early, nowing that

his post$release cost would rise. *nly &very and his management could estimate the ris of releasing

early.

:se the pre$release fix costs to see if you and your staff are being cost$effective in your pre$release

activities. I!ve found that each organiation has a typical post$release cost, not necessarily tied to the

pro"ect. %o I use the post$release cost to help define release criteria. This helps you manage the ris

of too many defects to fix after the release.

Dnowing how much it costs you to find and fix a defect allows you to as -uestions about how you!re

finding, fixing, and verifying defects. 0et another way to build a system with the appropriate -uality.

About the AuthorJohanna Rothman observes and consults on managing high$technology productdevelopment, looing for the leverage points that will mae her clients more successful. Johanna was

the 'onference 'hair for %E!s %oftware Fanagement 1%F2 'onference 1$9 Geb.2. %he conducted

a management$improv tutorial and participated in a panel discussion of mentoring and manager$

maing at the conference. %he recently co$moderated a RoundTable HFaing the Transition to

Fanagement with sther #erby. 0ou can reach Johanna at "r"rothman.com or by visiting

www."rothman.com. Bac to Top
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Reaer Comments &dd 0our 'omments Bac to Top

I would lie to than the author for introducing a more up to date metric for calculating the cost of

a defect. IKve always compared defects costs to the JA7 study from the early L/s, that for every

earlier stage in the development cycle one can catch and remediate a sw defect, a savings of /x

is achieved 1for e.g., /,/// to fix a sw defect once in testing, down to 8/ if caught while writing

the code itself2. IKm going to tae another loo at the white paper, MGrom %oftware Euality 'ontrol

to Euality &ssuranceM with renewed eyes. Implementing proactive -uality assessment and

assurance tools, plus the use of impact analysis tools may save an organiation even more

money than I once imagined. Thans again.....1/


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time did &veryKs team waste fixing bugs in code that was eventually eliminated or radically

rewritten before code completeC


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combination with the effort of testing re-uired to find the defect to be fixed. Testing and

debugging, whoever does the actual wor, are two different activities with their own metrics and

implications. Gor example, if one team finds and fixes // defects and the other team finds ;//

defects and fixes //, all else being e-ual, the second team is at a much greater advantage. It

means they have had the opportunity to fix the highest priority defects first, and have a better

basis to calculate the ris of releasing with the nown unfixed defects. They also have information

about nown defects and worarounds to put in the readme or to eep in the customer support

database. The number that stics out in my mind about the relative cost of fixing a defect in

production vs. discovering it at the re-uirements phase, when the defect was traced bac to faulty

re-uirements, is . & new person is debugging someone

elseKs code. & -uestion I have too is, when #anKs team decides not to fix bugs until month L, does

this mean also that they are not unit and integration testing either until month LC If not, they are

wasting the opportunity to do the testing when their mind is fresh on the specs and how they

implemented them. IKm not sure if my comments miss the point of this article, but I feel it is

important to 2encourage developers to do unit and integration testing before system testing in

any case 1even internal system testers can get crany when a system has too many bugs2 and


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views) . It doesnKt matter in my opinion how many days it taes to fix a problem. #evelopers wor

on many activities in a day and duration canKt be calculated by elapsed days. What matters a lot is

the effort it has taen 1in terms of actual hours the developer spent woring for the fix. Fany

defect tracing tools now have a seperate field where the effort in hours can be entered for each

defect. We can run a -uery to find out the total hours, get the actual number of days and use it in

the calculation.

what does it cost to fix a defect

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