Can anybody guide me how to handle the negative results which may arise during the 3 sigma trending. when i get a negative result, is i have to neglect that or i have to consider that?

3-sigma formula is used to define the trend limits only. Please explain the issue properly.

Hello Mr. Ankur,

Lets say i have to do a 3 sigma trending for X-quality parameter as per the below details

now in the above example , i have got a negative value for Sigma lower limit (As Average value is smaller than sigma value) in this case how to consider sigma value. whether i have to neglect negative value and i have to consider positive result OR i have to consider negative result itself?

if i consider negative result then i am not able to identify OOT as the trend will show all the result well within the 3 sigma trend.

could you please suggest anything on this and also please let me know is there specific guideline is there for “handling and investigation of out of trend or outlier”

Regards

Santhosh T S

@santhutudur First of all read the following article to understand the 3 sigma properly. There is no way to find the negative results.