Knowledge that Transforms

Algorithmically recommending workers to employers for the purpose of recruiting can substantially increase hiring: in an experiment conducted in an online labor market, employers with technical job vacancies that received recruiting recommendations had a 20% higher fill rate compared to the control. There is no evidence that the treatment crowded out hiring of nonrecommended candidates. The experimentally induced recruits were highly positively selected and were statistically indistinguishable from the kinds of workers employers recruit “on their own.” Recommendations were most effective for job openings that were likely to receive a smaller applicant pool.

Social networks are important for finding jobs, but which ties are most useful? Granovetter has suggested that “weak ties” are more valuable than “strong ties,” since strong ties have redundant information, while weak ties have new information. Using 6 million Facebook users’ data, we find evidence for the opposite. We proxy for job help by identifying people who eventually work with a pre-existing friend. Using objective tie strength measures and our job help proxy, we find that most people are helped through one of their numerous weak ties but a single stronger tie is significantly more valuable at the margin.

This paper estimates peer effects in a university context where students are randomly assigned to sections. While students benefit from better peers on average, low-achieving students are harmed by high-achieving peers. Analyzing students’ course evaluations suggests that peer effects are driven by improved group interaction rather than adjustments in teachers’ behavior or students’ effort. Building on Angrist’s research, we further show that classical measurement error in a setting where group assignment is systematic can lead to a substantial overestimation of peer effects. However, when group assignment is random—like in our setting—peer effect estimates are biased toward zero.

Editor's Note Our policy is to annotate all English-language books on economics and related subjects that are sent to us. A very small number of foreign-language books are called to our attention and annotated by our consulting editors or others. Our staff does not monitor and order books published; therefore, if an annotation of a book does not appear six months after the publication date, please write to us or the publisher concerning the book.

The categories listed below are used to classify books, book reviews, journal articles, and dissertations indexed in JEL, JEL on CD, EconLit, and www.e-JEL.org . New changes to the classification system appear as soon as possible on www.econlit.org . The JEL classification system may be used freely for scholarly purposes. We suggest the following format: “JEL: A10, B10, etc.”

Editor's Note Our policy is to annotate all English-language books on economics and related subjects that are sent to us. A very small number of foreign-language books are called to our attention and annotated by our consulting editors or others. Our staff does not monitor and order books published; therefore, if an annotation of a book does not appear six months after the publication date, please write to us or the publisher concerning the book.

The categories listed below are used to classify books, book reviews, journal articles, and dissertations indexed in JEL, JEL on CD, and EconLit. New changes to the classification system appear as soon as possible on www.econlit.org . The JEL classification system may be used freely for scholarly purposes. We suggest the following format: “JEL: A10, B10, etc.”

The categories listed below are used to classify books, book reviews, journal articles, and dissertations indexed in JEL, JEL on CD, and EconLit. New changes to the classification system appear as soon as possible on www.econlit.org . The JEL classification system may be used freely for scholarly purposes. We suggest the following format: “JEL: A10, B10, etc.”