The four quality assurance steps within the PDCA model stand for:

• Plan: Establish objectives and processes required to deliver the desired results.
• Do: Implement the process developed.
• Check: Monitor and evaluate the implemented process by testing the results against the predetermined objectives
• Act: Apply actions necessary for improvement if the results require changes.

PDCA is an effective method for monitoring quality assurance because it analyzes existing conditions and methods used to provide the product or service customers. The goal is to ensure that excellence is inherent in every component of the process. Quality assurance also helps determine whether the steps used to provide the product or service are appropriate for the time and conditions. In addition, if the PDCA cycle is repeated throughout the lifetime of the product or service, it helps improve internal company efficiency.

(source : wisegeek.com)