A preliminary report is an evaluation that discusses in depth, the findings on a particular specimen/subject. Data is gathered from the subject in order to make a determination. A preliminary report is not the final results on a subject but rather an analysis.
Write an introduction, giving an overview of your subject.
Discuss your research methods by including any observations, interviews or samples.
Write the preliminary results explaining any realizations or insights found during the research of the subject.
Discuss any results, new information and questions raised or found during the investigation.