There are usually many different titles such as certificationism, diploma theory, filtering theory, queuing theory, screening hypothesis and so on. According to this theory, education is only a screening device, or a means of selection or marking, which helps employers identify job seekers with different abilities and arrange them to fill corresponding jobs according to their abilities. Emphasize the importance of academic diplomas, and think that academic qualifications only reflect an individual's existing abilities through a paper diploma, but do not increase personal abilities; Screening is the main economic value of education; The positive correlation between education and wages is established through screening. It is generally believed that Spencer is an important representative of this theory. He mainly analyzes the market where signals work. In his view, workers with higher education are more productive than those without higher education, not because they go to college; On the contrary, the value of higher education lies in that it reveals or shows information about workers' productivity. He noticed that it is difficult for enterprises to accurately predict the future productivity of workers who are ready for employment, and it is also difficult for future employees to tell their employers their true productivity. Then, the employer must find effective information from the various characteristics of the job seeker to identify his ability. Among the observable attributes that constitute the overall image of job seekers, one is the logo and the other is the signal.
Logo generally refers to the inherent unchangeable characteristics of job seekers, such as gender, race, age, family background and so on. Signals refer to characteristics that are not innate and can be changed, such as education level and marital status. Education is a signal and a way for people to convey unobservable productivity to their future employers. However, if education is to become an effective signal, it must have another feature, that is, there must be a negative correlation between the cost of obtaining the signal and the actual productivity. In this way, other factors being equal, people with higher ability have lower education cost, can obtain higher education level, and are considered more productive by employers because of their higher education level, thus obtaining higher wages. On the other hand, because employers choose workers according to educational signals and pay corresponding wages, it will also encourage individuals to invest in education and increase employment opportunities.