There are three different sources from which an appraiser can verify that did the organization follow process or not.
Instruments: - It is a survey or questionnaire provided to the organization, project or individuals before starting the assessment. So that before hand appraiser knows some basic details of the project.
Interview: - It’s a formal meeting between one or more members of the organization in which they are asked some questions and the appraiser makes some judgments based on those interviews. During the interview the member represents some process areas or role which he performs in context of those process areas. For instance the appraiser may interview a tester or programmer asking him indirectly what metrics he has submitted to his project manager. By this the appraiser gets a fair idea of CMMI implementation in that organization.
Documents: - It’s a written work or product which serves as an evidence that a process is followed. It can be hard copy, word document, email or any type of written official proof.
Below is the pictorial view of sources to verify how much compliant the organization is with CMMI.
Figure: - Different data source for verification