Suboptimal utilization of labour, also termed sub-employment. Visible under-employment involves working fewer hours than a person normally works, or prefers to work. Invisible under-employment involves under-utilization of a person's skills, qualifications, or experience in a job that is lower grade than their usual job, or involves a skills mismatch, and may lead to low productivity and low income. The majority of part-time jobs are taken voluntarily in preference to full-time jobs, and so do not constitute visible under-employment. However, part-time jobs often involve invisible under-employment, for example when they are taken by women who revert to less skilled work on their return to the labour-market after an absence for child-rearing.