Wrong standard deviation calculation in AIAG SPC manual?

B

Bromus

Registered
#1
#1
Hello,

According to IATF 16949 I wanted to validate my worksheet for Cp/Cpk, Pp/Ppk calculations. I have used data set from page 186 of AIAG SPC edition 2 manual. Everything seems to be fine except of total sigma. My calculation is 0,188657 but in the manual there is 0,189037. I copied the data by hand from the manual, so I searched for a bug for a long time, but didn't find it. Additionally, total mean and sigma for within variation (Rbar/d2) is correct in my calculations based on copied data.

Does this mean there is a mistake in the manual? I realize that this is not a very significant difference, but an auditor who wants to compare my calculations with the manual may question their correctness. Can you confirm my calculations ?
 
Download Free White Paper
Elsmar Forum Sponsor
John Predmore

John Predmore

Trusted Information Resource
#4
#4
One possible difference you could check out is the Standard Deviation of a population versus Standard Deviation from sampling. Khan Academy explains. You could check this theory by doing the calculations step-by-step with N and then with N-1. Or take the larger result and multiply by SqRoot(N)/SqRoot(N-1) and see whether you get the smaller result.
 
Miner

Miner

Forum Moderator
Leader
Admin
#5
#5
Bromus said:
Good one :) e.i. stdev.s.
BTW: Minitab returns the same result as Excel using the same AIAG dataset.
Click to expand...
I get the same results as you in both Minitab and Excel using the sample standard deviation (n-1). I also manually calculated it using their formula and got the same results as Minitab and Excel.
 
B

Bromus

Registered
#6
#6
John Predmore: Once again, no :) I have used correct formula for sample (division by n-1). Of course I have tried to calulacte stdev step-by-step using square root from sum of squares divided by n -1. Still the same.

I have to low "level" to attach the file with source data and calculation so I have asked admin to do it. So you can check it by yourself.
 
B

Bromus

Registered
#10
#10
Matt Savage said:
I was expecting to see an errata sheet here: that lists the error, but nothing is listed. Is this only page that lists the standard deviation with the supporting data?
Click to expand...
If you mean the manual - it is Appendix F with full case study, starting with dataset followed by step-by-step calulations leading to capability indices.
As far as I know there is no errata for SPC manual.
 
You must log in or register to reply here.
Thread starter Similar threads Forum Replies Date
Q Where did my Alignment go wrong? MCOSMOS Inspection, Prints (Drawings), Testing, Sampling and Related Topics 0
L Does a backdate form format can be changed if wrong revision is used? Document Control Systems, Procedures, Forms and Templates 8
G Gage R&R - Where am I going wrong? Part of a FAIR submission (Aerospace) Gage R&R (GR&R) and MSA (Measurement Systems Analysis) 2
Richard Regalado What could go wrong with information: Ransomware statistics and facts (2018 to present) IEC 27001 - Information Security Management Systems (ISMS) 0
L PPM - wrong parts or defective parts? IATF 16949 - Automotive Quality Systems Standard 18
Ed Panek ISOTECH TTI-10 found out of calibration - Calibration house was wrong? General Measurement Device and Calibration Topics 7
N How to ensure our employees don’t grab and use the wrong materials Manufacturing and Related Processes 11
Marc Quality (Industry) 4.0 - What could possibly go wrong? Coffee Break and Water Cooler Discussions 1
G What's wrong with this Shaft OD Gage R&R Gage R&R (GR&R) and MSA (Measurement Systems Analysis) 6
M Benchmarking Process Data - Man-day calculation gone wrong Benchmarking 5
S Definition Would a wrong definition constitute an Audit Finding? Definitions, Acronyms, Abbreviations and Interpretations Listed Alphabetically 3
kedarg6500 Gage R&R - Is my sheet calculation wrong? Gage R&R (GR&R) and MSA (Measurement Systems Analysis) 21
L Color measurements R&R: what's wrong with white? Gage R&R (GR&R) and MSA (Measurement Systems Analysis) 5
M What if information in predicate 510k is obviously wrong? Other US Medical Device Regulations 5
D Root Cause Analysis done on the wrong observation Problem Solving, Root Cause Fault and Failure Analysis 9
L How to document use of wrong engineering drawing Inspection, Prints (Drawings), Testing, Sampling and Related Topics 22
C FMEA DOGMA about Severity - Am I right or Wrong? FMEA and Control Plans 2
M Even the ASQ got it wrong, the Kano model Quality Tools, Improvement and Analysis 4
P What can go wrong in a Construction Project - NCRs in Construction Industry Nonconformance and Corrective Action 5
Jim Wynne APQP, or Why Things Always Go Wrong APQP and PPAP 0
B Does the recording of wrong entries amount to a nonconformity? Records and Data - Quality, Legal and Other Evidence 7
J Stacked Line Chart - Am I using the wrong chart for the job? Statistical Analysis Tools, Techniques and SPC 11
T Preventing Wrong Terminal Crimped on a Wire Harness Manufacturing and Related Processes 7
Q What's wrong with my data? MSA result showed very high % R&R Gage R&R (GR&R) and MSA (Measurement Systems Analysis) 4
Rameshwar25 MSA Manual 4th Edition, Page 100 - What is wrong in the Linearity graph? Gage R&R (GR&R) and MSA (Measurement Systems Analysis) 8
Y P chart - wrong equations? Statistical Analysis Tools, Techniques and SPC 3
bobdoering Capability Calculations: Are AIAG SPC Appendix F Conclusions Wrong? Imported Legacy Blogs 5
Marc Newsweek admits how wrong they were about the internet After Work and Weekend Discussion Topics 5
Ajit Basrur Chilean mint spells country's name wrong on coins Nonconformance and Corrective Action 8
bobdoering Dr Wheeler weighs in on "Individual Charts Done Right and Wrong" Statistical Analysis Tools, Techniques and SPC 2
M Requirements for Changing Documentation to correct typos or wrong word selection Document Control Systems, Procedures, Forms and Templates 15
P How to prevent the LED wrong polarity when insertion on the production line? Problem Solving, Root Cause Fault and Failure Analysis 8
Marc SANS Report Says Organizations Focusing On the Wrong Security Threats After Work and Weekend Discussion Topics 0
M How do you identify the wrong orientation in complex wiring harness? Manufacturing and Related Processes 21
E Identification of out-of-process parts - Using the wrong tag Nonconformance and Corrective Action 2
C FDA delaying notification of receipt of 510(k)'s - What wrong with FDA? - China US Food and Drug Administration (FDA) 3
R WRONG Use of P-Chart Statistical Analysis Tools, Techniques and SPC 6
BradM What's wrong with this picture? Funny Stuff - Jokes and Humour 10
P Device Master Record requirements - wrong approach? ISO 13485:2016 - Medical Device Quality Management Systems 1
S Wrong material Ordered - Which Procedure and Form is relevant? Document Control Systems, Procedures, Forms and Templates 1
Jim Wynne Fish Pedicure--I must be in the wrong business Coffee Break and Water Cooler Discussions 9
B Is Minitab technical support answer 2255 wrong? Using Minitab Software 5
L Corrective action following a wrong answer of the auditee ISO 9000, ISO 9001, and ISO 9004 Quality Management Systems Standards 19
P First ISO13485 accreditation audit: What are things that can go wrong? ISO 13485:2016 - Medical Device Quality Management Systems 4
M Wrong Calibration / Verification Result - Height gauge IATF 16949 - Automotive Quality Systems Standard 6
Wes Bucey Oops! Opportunity for mistake proofing? Worker flicks wrong switch World News 14
N TGR (Things Gone Right) & TGW (Things Gone Wrong) reports - Seeking form or checklist Document Control Systems, Procedures, Forms and Templates 9
Marc 'Wrong site' surgeries and other mistakes on the rise World News 15
W Mr. Ford's Wrong Turn - Why U.S. Automakers Can't Blame Japan World News 0
P No In-process or first piece inspection - Final Inspection ONLY! Am I wrong? Inspection, Prints (Drawings), Testing, Sampling and Related Topics 37

Similar threads

Top Bottom