A part-time job is a form of employment that carries fewer hours per week than a full-time job. They work in shifts. The shifts are often rotational. Workers are considered to be part-time if they commonly work fewer than 30 hours per week. According to the International Labour Organization, the number of part-time workers has increased from one-quarter to a half in the past 20 years in most developed countries, excluding the United States. There are many reasons for working part-time, including the desire to do so, having one's hours cut back by an employer and being unable to find a full-time job. The International Labour Organisation Convention 175 requires that part-time workers be treated no less favourably than full-time workers.