In Process control chart, we consider the process is out of control if there're 7 consecutive results aligned one side from the average beam.my question is why specifically seven points exact? Saving Changes...
7 in consequence eliminates any random or coincident. Also it has a connection to the following :
Two points together are more than mean (2)+(2*sigma), but less than mean + (3*sigma)
I am not sure about the last I need to review my probability math from my quantitive studies. Saving Changes...
Drew CraigSr. Agile & Product Coach| VanguardPhiladelphia, Pa, United States
Additionally, so as to not be captured as a false-positive or anomaly. Saving Changes...
I believe this is based on the assumption that you are dealing with a normal distribution in which case 50% of outcomes should be on one side or the other. As such, the probability of getting seven points above or below the mean would be .5^7 which is a pretty small likelihood and hence wouldn't be consider normal variation.
Please note that this is just one rule of seven - there are about six or seven other ones (e.g. seven consecutive observations increasing or decreasing progressively) - the seven above or below the line is just a very common one.
Kiron Saving Changes...
Sergio Luis ConteHelping to create solutions for everyone| Worldwide based OrganizationsBuenos Aires, Argentina
These are some old rules which were set by a company several years ago. It has to do with some basic calculation for errors and experiences. Now, you have other options and calculations can be used instead of those for your specific process. However, in most of the times and for general purposes, some of these rules can be applied. Saving Changes...
