# Capability Analysis - Unusual Statistical Distribution of my Proccess

J

#### Jparfer

Hi there!

I have a big problem with my process. I want to see the distribution that my proccess have, but its not belong to a known distribution.

How can i stimate capability with less than 100 data using not distribution supossion?

Thanks!

T

#### t.PoN

Re: Statistical Distribution of my proccess

Use histogram to figure out what is your distribution.
the ASQ has nice excel sheet to help you doing your job. i have attached them below, i hope they can help

#### Attachments

• 72 KB Views: 200
• 1 MB Views: 391
Last edited by a moderator:

#### Bev D

##### Heretical Statistician
Staff member
Super Moderator
Are you required by your Customer to report a Cpk or Ppk number? Or are you genuinely intereseted in your process capability?

what is your process? what feature, property or function are you measuring?

The best way to understand your process capability to plot the data in time series agianst the spec limits. A simple run chart if there is only value per part or a multi-vari if there are multiple values per part. This is the starting place and the most informative. once you understand the nature of yoru process you can proceed to histograms and control charts...

If you post your data, we can provide more specific help

#### Steve Prevette

##### Deming Disciple
Staff member
Super Moderator
Also, you can still use SPC to determine if the process is stable and for the basis of capability calculations as SPC is non-parametric.

S

#### supreecha

Re: Statistical Distribution of my proccess

Comparision Sheet by Excel , Minitab & Crytal Ball .

#### Attachments

• 1 MB Views: 369
• 1.9 MB Views: 349
Last edited by a moderator:

#### bobdoering

Trusted Information Resource
Attached is distribution analysis that shows clearly that you do not have a normal distribution. That said, we know that the regular Cpk and Ppk calculations may not be applicable.

The real question is: should this characteristic be non-normal? Does it make sense? The only way to determine that is understanding the process. Since we do not have any idea what the process is, very little can be discerned about whether it is stable or in control at this point.

#### Attachments

• 77.2 KB Views: 168
Two excellent examples of process capability analysis from Quality Magazine Capability, Accuracy and Stability - Processes, Machines, etc. 5
Capability analysis - What is going on this chart? Manufacturing and Related Processes 15
A Capability Analysis for Packaging Seal Strength with spec. >0.1 Kgf using Minitab Using Minitab Software 6
C Minitab Binomial Process Capability Analysis Chart Explanation Using Minitab Software 1
C P value not greater than 0.05 for Capability Analysis Statistical Analysis Tools, Techniques and SPC 3
M Sample size when conducting capability analysis with OK and NOK parts Statistical Analysis Tools, Techniques and SPC 3
R Capability Analysis (using Histogram) for Subgrouped Data Statistical Analysis Tools, Techniques and SPC 16
A Inspection Capability Study (Kappa Analysis / Attribute R&R) as Certification Req't Training - Internal, External, Online and Distance Learning 7
C Process Capability - Attribute Data Analysis (Template) Document Control Systems, Procedures, Forms and Templates 0
C Process Capability - Variables Data Analysis (Template) Document Control Systems, Procedures, Forms and Templates 0
A Cnpk (Non-Parametric Capability Analysis) to assess whether the Process is Stable Capability, Accuracy and Stability - Processes, Machines, etc. 7
Q JMP Measurement Capability Analysis Gage R&R (GR&R) and MSA (Measurement Systems Analysis) 1
P Data Analysis - Johnson Transformation/Weibull Distribution/Capability Analysis Capability, Accuracy and Stability - Processes, Machines, etc. 15
L Capability Analysis - Help with Minitab results Using Minitab Software 15
Capability Analysis for Limited Resolution (thickness of sheets) Capability, Accuracy and Stability - Processes, Machines, etc. 6
M Capability Analysis and Sample Size Capability, Accuracy and Stability - Processes, Machines, etc. 8
B Capability Analysis of a Repeated Feature Quality Tools, Improvement and Analysis 9
B Capability Analysis of a Small Sample Size (as small as 2 and as large as 30) Statistical Analysis Tools, Techniques and SPC 14
S "Normal" vs. "Between/Within" Capability Analysis Capability, Accuracy and Stability - Processes, Machines, etc. 2
S How to conduct Capability Analysis for this data? Statistical Analysis Tools, Techniques and SPC 12
S Free or Opensource Software that can do Multivariate Capability Analysis Statistical Analysis Tools, Techniques and SPC 8
T Capability Analysis in the Real World Capability, Accuracy and Stability - Processes, Machines, etc. 7
D Capability Analysis for Packing Process in Food Manufacturing Capability, Accuracy and Stability - Processes, Machines, etc. 11
I Machine Capability Analysis in Multi-Dimensional Cases Capability, Accuracy and Stability - Processes, Machines, etc. 2
A Yearly MSA (Measurement System Analysis) & Capability Study - TS 16949 Requirements Gage R&R (GR&R) and MSA (Measurement Systems Analysis) 2
S Capability Analysis of Non-Normal Data Statistical Analysis Tools, Techniques and SPC 23
Process Capability Analysis Binomial or Normal using Minitab 15 Using Minitab Software 54
P Capability Analysis in Minitab - Subgroup size Misc. Quality Assurance and Business Systems Related Topics 2
J Capability Analysis (Cpk) of torque driver process Capability, Accuracy and Stability - Processes, Machines, etc. 5
E Process Capability Analysis for a Service Company ISO 9000, ISO 9001, and ISO 9004 Quality Management Systems Standards 7
H Regarding: Describing Graphical Overview and Capability Analysis for main dept leader Quality Manager and Management Related Issues 1
M Macro that will perform a normality test and capability analysis - Minitab help Using Minitab Software 1
C Does a Chronically Unstable Process need a Capability Analysis? Statistical Analysis Tools, Techniques and SPC 10
F Multi Capability analysis with MINITAB Using Minitab Software 2
A Whats the rationale for a Sample size of 30 for Capability Analysis? Statistical Analysis Tools, Techniques and SPC 5
D Normal vs. When a Between / Within Capability analysis should be used? Statistical Analysis Tools, Techniques and SPC 12
A Capability Analysis - Dealing with non-normal data in Minitab Using Minitab Software 8
E MSA vs. Measurement Capability Analysis - What are the differences? Gage R&R (GR&R) and MSA (Measurement Systems Analysis) 33
J What causes Ppk to be greater than Cpk when a basic capability analysis is run? Capability, Accuracy and Stability - Processes, Machines, etc. 17
A Sample size for Capability Analysis in PPAP APQP and PPAP 2
L Definition Cp Cpk Pp and Ppk Definitions - I'm doing SPC and Capability Analysis Definitions, Acronyms, Abbreviations and Interpretations Listed Alphabetically 7
Capability in sewing processes CP,CPk,PP,PPk Capability, Accuracy and Stability - Processes, Machines, etc. 2
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 6
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
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 Data for Paint Thickness on Painted Parts Statistical Analysis Tools, Techniques and SPC 10