# ?Pa? Capability Index - Has anyone ever heard of this?

D

#### debun

I got a spread sheet from a vendor where they calculated a capability in excel called ?Pa? I know of Pp and Cp but I have never heard of Pa. The excel formula calculated it using the absolute value of ? - center value = (USL+LSL)/2 divided by 3σ so in summary ?-center value / 3σ. Anyone ever heard of this?

#### Stijloor

Super Moderator
Re: ?Pa? capability index, has anyone ever heard of this?

A Quick Bump!

Can someone help?

Thank you very much!

T

#### t.PoN

I always thought capability index is used only for normal distribution.
which means: Center Value = μ!

One possible interpretation is the Probability of Acceptance! but still the formula doesn't add up

Last edited by a moderator:
D

#### debun

I always thought capability index is used only for normal distribution.
which means: Center Value = μ!

One possible interpretation is the Probability of Acceptance! but still the formula doesn't add up
I don't think I was very clear

center value = (USL+LSL)/2
μ = mean of the population or in this case sample mean

Pa = (?-center value )/3σ

#### Bev D

##### Heretical Statistician
Super Moderator
I've not heard of it - but then I tend to disregard any literature on the capability indices.

The math is simple, but I'm not really sure of it's value: the formula just results in a ratio of the distance of the mean of the process from the center of the specification to the spread of the individual values. without a comparison to the specifications there is no way to know if the process is 'good' or 'bad'.

Did they provide you with any 'acceptable number?

Or is this just an interim calculation that is used in another formula?

D

#### debun

I've not heard of it - but then I tend to disregard any literature on the capability indices.

The math is simple, but I'm not really sure of it's value: the formula just results in a ratio of the distance of the mean of the process from the center of the specification to the spread of the individual values. without a comparison to the specifications there is no way to know if the process is 'good' or 'bad'.

Did they provide you with any 'acceptable number?

Or is this just an interim calculation that is used in another formula?
They just have a cell called "Pa" with Chinese 準確度 which according to Google translate means accuracy. It is not used in any other calculations and no acceptance criteria for the value.

They have the same Chinese characters for the "Pp" cell, but of course the formula is different.

Converting Defect Rate To Capability index Capability, Accuracy and Stability - Processes, Machines, etc. 11
S Auto-Correlated Data and Capability Index Quality Tools, Improvement and Analysis 5
S Cpkm capability index: Make sense when the target is the lower tolerance limit? Statistical Analysis Tools, Techniques and SPC 9
J Heat treatment inspection and Process capability index Cpk Inspection, Prints (Drawings), Testing, Sampling and Related Topics 2
R Capability Index for Furnaces - CQI-9 Assessment Capability, Accuracy and Stability - Processes, Machines, etc. 1
R How to measure Machine Capability index Cpm Statistical Analysis Tools, Techniques and SPC 1
G What does a Process Capability Index of greater than 1 suggest? Capability, Accuracy and Stability - Processes, Machines, etc. 3
S What Capability Index should I use? SMT Application Capability, Accuracy and Stability - Processes, Machines, etc. 13
C Composite Process Capability Index - Cpk is not additive Capability, Accuracy and Stability - Processes, Machines, etc. 3
V Machine short term capability study with Cmk index in automotive industry Capability, Accuracy and Stability - Processes, Machines, etc. 3
Q Confused about the machine capability index Cmk Capability, Accuracy and Stability - Processes, Machines, etc. 1
A Acceptance criteria for Cmk (machine capability index) Statistical Analysis Tools, Techniques and SPC 3
P What does TCI mean? Test Capability Index = USL-LSL/6*sigma of the test only Gage R&R (GR&R) and MSA (Measurement Systems Analysis) 5
S Cmk is defined as a Capability Index for a Stable Machine Capability, Accuracy and Stability - Processes, Machines, etc. 8
C Capability index for one-sided specification? Cpk(max) = (USL-Xbar)/3*s ?? Capability, Accuracy and Stability - Processes, Machines, etc. 13
A Unilateral Tolerance Capability - Shaft Runout - Which capability index to use? Statistical Analysis Tools, Techniques and SPC 2
A What is Cgk? (Index of Testing Means Capability) Statistical Analysis Tools, Techniques and SPC 18
Capability of a roughness gauge Gage R&R (GR&R) and MSA (Measurement Systems Analysis) 3
Calibration / Capability in a PCP FMEA and Control Plans 1
QSB+ : capability of measurement equipment IATF 16949 - Automotive Quality Systems Standard 15
Process capability analysis in ISO 9001:2015 ISO 9000, ISO 9001, and ISO 9004 Quality Management Systems Standards 3
Data normality versus capability Capability, Accuracy and Stability - Processes, Machines, etc. 11
Capability calculation of surface profile Capability, Accuracy and Stability - Processes, Machines, etc. 20
Understanding Capability and Control Charts Series Using SQCpack Software 0
Control Charts & Capability Analysis 101 Using SQCpack Software 0
Process Capability - Determining the process capability of certain equipment Lean in Manufacturing and Service Industries 6
Initial capability studies on similar parts APQP and PPAP 7
Capability Study for Leak Tester Capability, Accuracy and Stability - Processes, Machines, etc. 9
Capability in sewing processes CP,CPk,PP,PPk Capability, Accuracy and Stability - Processes, Machines, etc. 10
Machine Capability Capability, Accuracy and Stability - Processes, Machines, etc. 2
How to Establish the Calibration & Measurement Capability (CMC)? ISO 17025 related Discussions 1
How to keep the manufacturing capability under the API monogram Oil and Gas Industry Standards and Regulations 7
Minitab Capability of the Population (no sampling) Using Minitab Software 11
Capability Study - in the beginning of your career what should you have known about the tool Quality Tools, Improvement and Analysis 11
Two excellent examples of process capability analysis from Quality Magazine Capability, Accuracy and Stability - Processes, Machines, etc. 5
Capability study with a minimum spec Statistical Analysis Tools, Techniques and SPC 8
Capability - CPk comparison values Capability, Accuracy and Stability - Processes, Machines, etc. 12
Capability analysis - What is going on this chart? Manufacturing and Related Processes 15
Capability Data for Paint Thickness on Painted Parts Statistical Analysis Tools, Techniques and SPC 10
Is capability applicable for a destructive test? Capability, Accuracy and Stability - Processes, Machines, etc. 9
Capability or Gage R&R Study for Leak Tester? Reliability Analysis - Predictions, Testing and Standards 15
Pre-Production Capability Assesment Reliability Analysis - Predictions, Testing and Standards 5
Iec 60601 Impedance and current-carrying capability IEC 60601 - Medical Electrical Equipment Safety Standards Series 1
Machine Setup for a CNC Machine Capability Study Capability, Accuracy and Stability - Processes, Machines, etc. 1
O Ring capability and measurement - What is the automotive 'norm' for capability studies on O Rings? General Measurement Device and Calibration Topics 3
Measuring Capability of Process with Multiple Specifications Capability, Accuracy and Stability - Processes, Machines, etc. 6
Capability Study for Tapped Hole Reliability Analysis - Predictions, Testing and Standards 3
Sampling for capability studies for variables and attributes Capability, Accuracy and Stability - Processes, Machines, etc. 4
L How to evaluate the process capability of a data set that is non-normal (cannot be transformed and does not fit any known distribution)? Capability, Accuracy and Stability - Processes, Machines, etc. 14
Final process capability results - What I am supposed to present? Cp and CpK? APQP and PPAP 11