What is Six Sigma?

Six Sigma is a performance improve-ment methodology that seeks to identify the key sources of variation in a process(critical factors) that cause defects to occur. By mapping processes, measuring their output, and analyzing its many input variables, Six Sigma determines how to optimize the output from a process by controlling the inputs. Six Sigma projects move through a disciplined framework (known as 'DMAIC')

Define the problem – in terms of performance, consequences and gaps from what is desired 

Measure the process – first to ensure the data is reliable, then to decide how well the process performs 

Analyze the variables – using statistical tests of significance, to find those variables that have the greatest impact on process yield

Improve the process – through small scale experiments and hypothesis tests to compare the impact, before and after

Control the process – to sustain gains and ensure process does not regress to previous levels

The term “Six Sigma” refers to the level of perfection such a process will deliver. Specifically, a “Six Sigma process” allows for six standard deviations between the average  performance  of  the  process and  its nearest  specification  limit.  This process  will  produce  defects  only  3.4 million times per million occurrences (3.4 DPMO)  and  is  regarded  for  all  practical purposes to be “a perfect process.”

Read a full review article on Six sigma in pharmaceutical industry.

Source: Jean Cherry, Sridhar Seshadri, “Six Sigma: Using Statistics to Reduce Process Variability and Costs in Radiology,” Radiology Management, Nov/Dec 2000