What's a Thesis? Academic research by university academics; lecturers and researchers (e.g. a PhD, MPhil, MRes) and you may reference this level of research in your work
What's a Dissertation? Academic research by university undergraduate or postgraduate students (e.g. BA, MA, MSc). They are not a published source and you would not normally reference a student's dissertation in your university work. Instead you may consider the reference lists they have presented, find some of those sources, read, analyse, interpret and maybe reference them yourself.
This resource supports research at all levels, providing material to guide users through each stage of the research process.
Tip: Also try entering other search word combinations in the catalogue to find relevant books e.g. 'interview skills', 'interview techniques', 'focus groups' and 'survey research methods'.