# six sigma in relation to process duration

Submitted by mwaserma@gmail.com on Mon, 12/29/2014 - 17:34

Would it be possible to elaborate a little on the relation between six sigma quality requirement and process duration?

I am looking at the question that has 13 days of the PERT task duration estimate and 1 day as a standard deviation. The correct answer reads that the task can be completed from 7 to 19 days period. I don't really understand where 6 days duration deviation came from...

Any input is greatly appreciated.

admin

Wed, 12/31/2014 - 11:09

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## Question is not clear

Question is not clear

mwaserma@gmail.com

Tue, 01/06/2015 - 16:26

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## Six Sigma

Just to clarify the question I am struggling with...

The activity has an optimistic estimate of 10 days, pessimistic estimate of 16 days and most likely estimate of 13 days. If your company has a quality requirement of Six Sigma what is the duration within which task must be completed?

I calculated 13 days mean.. and standard deviation = 1. Correct answer is 7 - 19 days. I don’t understand why it is +- 6 days from the mean.

Thanks.

kniraj

Thu, 01/08/2015 - 04:37

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## I will make an attempt. Will

I will make an attempt. Will request the experts on this forum to review once.

Your Estiated Duration (ED) for this will be (O+4M+P)/6 = 13

Your Standard Deviation (SD) will be (P-O)/6 = 1

6 six sigma will be 6SD which is 6*1 = 6

Range = ED + SD and ED - SD

So you get 13-6 to 13+6 which is 7 to 9 days

mwaserma@gmail.com

Sat, 01/10/2015 - 13:14

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## Six Sigma

I think that I still don't understand the part "6Sigma will be 6 SD". Why would you translate level of quality Six Sigma into broader effort period to perform the task?

sanathsh

Sun, 01/11/2015 - 16:11

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## 6 Sigma supposed to be even closer to estimate?

How does it make sense ?

6*SD for 6 Sigma , and 3*Sd for 3 Sigma. Isnt 6 Sigma supposed to be more closer to the estimate.

philzs

Mon, 01/12/2015 - 02:29

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## this is a good question that

this is a good question that I would like to know also, if it's Standard deviation * 6 for six sigma and Standard Deviation *3 for three Sigma, 3 sigma will be more acurate, which sounds weird to me ?

Shaan23

Tue, 01/13/2015 - 01:11

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## It is a range

It is a range and 6 Sigma will be more accurate than 3 sigma. If you go by numbers the confusion is bound to be there, since you just see one number as 3 times and second as 6 times.

Consider the same example, Estimated duration is 13 days, So what is the probablity of completing the activity in the range of 10-16 days which is +-3 sigma. Obviously the confidence level of completing the activity within 10-16 days is less as compared to completing in 7 to 19 days.

This is the precise reason why 6 sigma is more accurate than 3 sigma.

kniraj

Fri, 01/16/2015 - 03:37

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## Take a look at the below

Take a look at the below articles as well... to get some more understanding of the six sigma.

http://www.deepfriedbrainproject.com/2010/08/standard-deviation-project-...

http://www.dummies.com/how-to/content/basic-statistics-you-should-know-f...

pmalik

Mon, 06/12/2017 - 08:28

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## For 6 sigma, range will be 7

For 6 sigma, range will be 7-19 days. For complete explanation on PERT and SD, you can read following articles

* PERT Formula and Use of Standard Deviation

* How to use PERT, CPM and Standard Deviation Together?