primary source: source which has the original source of information. It is a source of which has been created when the study is done.
Secondary source: in which analysis is done based on the primary source, In this original information analyzed and arranged after that evaluation is done.
In this case an interview conducted by a research writer would be a secondary source because the analysis is done based on the primary data.
tertiary source: It is a distillation of the information obtained from both primary and secondary sources.