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QA vs QC - what's the difference?

Many people think QA and QC are just interchangeable terms.  Not so.

Quality Control - QC

This is the most basic level of quality.  It started with activities whose purpose is to control the quality of products or services by finding problems and defects.

At its simplest, QC is inspecting, testing or checking something (service or product) to make sure it's OK.  The intent is to identify anything that isn't OK, and either fix it or eliminate it, to make sure it conforms to the specifications, and has/does/functions as required.  QC is typically done at the end of the line, before it 'goes out the door'. If the something isn't OK, this is called 'nonconformity' or a nonconforming service/product.

Service Example

Specifications:  A consulting company is hired to make an expert assessment of the safety systems, methods & procedures at a particular firm.  The deliverable is a written report that should include an assessment of whether the various systems & procedures are adequate, if there are any risks to the firm, and recommendations to address any identified risks or problems. 


Q:  Consider the following possible outcomes.  Which would be rejected as nonconforming? 

1. The delivered report contains information on all sections above; it is professionally written and presented. 

2. The report is delivered to the client, but somehow the last page was left out (final couple of paragraphs from the recommendations section).

3. The delivered report has information on all the required sections.  But it is badly written and poorly presented, below the standard that the consulting firm sets for its reports to clients.


A:  Only report 1 is OK.  The reports for 2 and 3 aren't. Report 2 is missing parts of a required section.  While Report 3 has all the agreed content wanted, its presentation doesn't meet the internal standards set and expected by the consulting company.


Product Example

Specifications are defined in a production plan & accompanying drawing. Each widget is to be made of a particular grade of steel, 5 cm x 3.5 cm, with 2 holes drilled into it (as per the drawing); it must be perfectly square, and have a smooth finish. 


Of 100 widgets coming off the production line, 98 meet these specifications, but two don't. One is 5cm x 3.4 cm, the other is 5 x 3.35 cm.  Both these widgets should be rejected as nonconforming. 



Quality Control, Assurance and Management
QC, QA & Management

Quality Assurance (QA)

Quality Assurance developed from the realisation that quality could be improved by looking 'further up the line'.  It is aimed at preventing nonconformities/defects.


QA still has QC at its core to control the quality of service/product, but it goes beyond mere testing or inspection to also consider related activities or processes (such as training, document control and audits) that may be resulting in defects further down the line.  


Think of QC as something like doing periodic checks to see that a horse is still in its stable, whereas QA would aim to make sure that the stable doors and gate locks work properly and that all the stablehands are trained and aware of the need to close and bolt doors properly.  


Service Example - QA

Using the same example as above, QA would aim to find out:

for Report 2. Why was the last page of the recommendations left out - eg, was this requirement not passed on to the consultant?  Or did it happen when the report went to the printing department?  And what must change to prevent it happening again?

Again, for Report 3: Why did these problems occur with the report - was it perhaps written by a new staff member or a contractor?  If so, why didn't they know the standards?  And why wasn't it checked before delivery?  What needs to change to stop this kind of thing happening again? 


Product Example - QA

What happened to make these two widgets fail?  The fault is in the same dimension, suggesting perhaps a similar cause.  Did a machine slip?  Is the machine wearing?  If the fault was in the machine, is the maintenance program perhaps inadequate?  And so on. 

Quality Management

As the quality movement matured and improved, it developed into Quality Management. Now the emphasis has widened to include developments in systems thinking and management systems.  Quality management is a much broader field.  While it includes quality planning, as well as quality control and quality assurance, it also includes quality improvement and extends beyond just QA and QC to a systems approach and looking at the quality management system as a whole.


The systems approach considers the various elements of the entire system.  In the 9001 model, this comprises five main components of:


Author: Jane Bennett

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