Capability Analysis

Capability can be assessed for either variable or attribute data collected either in the short-term or in the long-term. The process must be in control before you assess capability. If the process is not in control, then, the capability estimates will be incorrect.

• Assess capability for a quantitative/qualitative parameter

1. Verify the specification

The spec is ..., The tolerance is ..., Is it okay to ask the customer?

2. Collect a data sample

long-term or short-term?

qualitative parameter)

Count the occurrence of defects

Caluculate the proportion of defects

Caluculate Z-score

3. Calculate Cp, Cpk

qualitative parameter) change from Z to Cp, Cpk, etc

• Estimating Cp, Cpk

The short-term or long-term? -> Z-Shift

Z-Shift-> ZLT=ZST-1.5

*ST:short-term, LT:long-term

If the initial data was given as 3s in the short- term, the conversion to long- term would be as follows: 3s-1.5s=1.5s

Other conversion:Cpk=ZST/3, Ppk=ZLT/3, ZST=1.5+ZLT

Ref)

● Process capability index (Wikipedia)

● 6.1.6 What is Process Capability?

NIST/SEMATECH e-Handbook of Statistical Methods, http://www.itl.nist.gov/div898/handbook/

● Z Shift

-> isixsigma.com

● 工程能力分析－Capability Analysis (Japanense)

-> Back (This is the site of Japanese ver.)