Capability is the measure of how well a process is able to satisfy customer requirements. It assesses the process' ability to deliver consistently and output that meets customer specification.
Capability studies are undertaken to compare process performance relative to customer specifications, and are performed both when establishing a new process and on an on-going basis.
Preliminary capability studies are completed over a relatively short term to produce early information about the performance of a new or revised process.
On-going capability studies use performance data from a longer period. They provide a picture of the process that includes all common causes of variation over a number of sampling periods.
Capability is generally expressed in terms of capability indices. These identify the degree of the process capability, and the risk of producing non-conforming product.