Employers prefer to fill jobs without the expensive and time consuming advertisement and interview process, where possible. No more than around 5-20% of job openings are ever publicly announced; the hidden job market therefore covers 80-95% of the total employment market. Only by digging around and cold calling can such positions be uncovered.

Other techniques for uncovering hidden jobs include business, professional and social networking and associations, and personal recommendations from relevant people or organizations. Usually in any field of work information about jobs is available from individual employers, even if they don’t advertise.