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The Cambridge-Somerville Youth Study (CSYS) is a delinquency prevention experiment embedded in a prospective longitudinal survey of the development of offending. The CSYS is recognized as the first randomized controlled experiment in criminology, one of the earliest randomized experiments of a social program, and the earliest example of a longitudinal-experimental study with criminological outcomes.


The study was developed and directed by Richard Clarke Cabot (1868-1939), a professor of clinical medicine and social ethics at Harvard University. Planning began in 1935 and the delinquency prevention program officially started in June 1939. The CSYS is recognized as the first randomized controlled experiment in criminology, one of the earliest randomized experiments of a social program, and the earliest example of a longitudinal-experimental study with criminological outcomes.

The CSYS has been the subject of three major follow-ups: in 1948, by Edwin Powers and Helen Witmer; in 1956, by Joan and William McCord; and in 1975-79, by Joan McCord. A fourth follow-up is underway, tracing participants into old age (mid-80s to early 90s).


At the heart of the Cambridge-Somerville Youth Study is a program designed to prevent delinquency targeted on “pre-delinquent,” under-privileged boys. Referred to as “directed friendship,” the preventive intervention involved individual counseling through a wide range of activities and home visits. Counselors talked to the boys, took them on trips and to recreational activities, tutored them in reading and math, supported their participation in the YMCA and in summer camps, and encouraged them to attend church. Boys in the treatment group received the program for a mean average of 5.5 years. Boys in the control group did not receive any special services. The program ended in 1945.

The study began with 650 boys (later reduced to 506), ages 5-13 years (median = 10.5), from Cambridge and Somerville, Massachusetts. Rated as either “average” or “difficult,” the boys were recommended by local schools, welfare agencies, churches, and police. The boys were placed in matched pairs—“diagnostic twins”—and one member of each pair was chosen at random (on a coin toss) to be in the treatment group.

Follow-ups in 1948 and in 1956 indicated that the program had no measurable impact on official offending. In 1975-76 (mean age = 45 years), Joan McCord located records for 480 participants (or 95%) and conducted interviews with (or distributed questionnaires to) 347 of them. Continued data collection up to 1979 located records for a total of 494 participants or 98%.

This 30-year post-intervention follow-up revealed iatrogenic program effects. Comparisons between the treatment and control groups indicated that the treatment group had not fared better on any outcome, and fared worse on a number of key outcomes. The treatment group men were significantly more likely to:

  • Commit more than one crime (among those who committed at least one crime)
  • Suffer symptoms of alcoholism
  • Manifest signs of mental illness
  • Die at a younger age (prior to 35)
  • Suffer from at least one stress-related disorder, especially high blood pressure or heart trouble
  • Report their work as unsatisfying

McCord proposed and tested several hypotheses to explain the iatrogenic effects. Perhaps the most important of these was the peer deviancy hypothesis.

It is because of the pioneering research of Professor Joan McCord (1930-2004) that the Cambridge-Somerville Youth Study has become so well known in the field of criminology. This included her work on the 1956 and 1975-79 follow-ups as well as her voluminous scholarship resulting from this research.

It is also owing to her directorship of the study for more than 30 years (1956-59 and 1975-2004), her stewardship of the study during the intervening years, and her thorough tracing of participants and meticulous record keeping. The latter are directly responsible for maintaining the integrity of the experiment as well as making possible the 70-year follow-up and the investigation of other key research questions today.

More information on Joan McCord and the CSYS can be found at the American Society of Criminology’s Oral History Project  and at Freakonomics Radio.

Directed by Professor Brandon Welsh, a research team of SCCJ faculty and graduate and undergraduate students are investigating four key research questions:

  1. On intervention effects: Have the iatrogenic effects observed in middle age persisted up to old age?
  2. On criminal offending over the life-course: What are the long-term offending trajectories, patterns of desistance from offending, and duration of criminal careers of the study participants?
  3. On intergenerational effects: What have been the effects on the children of the study participants (the third generation)? Have the children of the treatment group men (compared to their control counterparts) also experienced undesirable outcomes?
  4. On historical significance: What is our historical understanding of the development of the CSYS and its influences on delinquency prevention and what are the lessons for today?

Brandon C. Welsh, Ph.D.
Professor and Study Director

Gregory M. Zimmerman, Ph.D.
Associate Professor

Alexis Yohros, M.A.
Doctoral Student and Joan McCord Doctoral Fellow

Steven N. Zane, Ph.D., J.D.
Assistant Professor, Florida State University

Contact Brandon Welsh at

Peer-Reviewed Journal Articles

Welsh, B.C., Yohros, A., Zane, S.N. (2020). Understanding iatrogenic effects for evidence-based policy: A review of crime and violence prevention programs. Aggression and Violent Behavior. DOI:

Welsh, B.C., Zane, S.N., Zimmerman, G.M., & Yohros, A. (2019). Association of a crime prevention program for boys with mortality 72 years after the intervention: A follow-up of a randomized clinical trial. JAMA Network Open, 2(3), e190782.

Welsh, B.C., Dill, N.E., & Zane, S.N. (2019). The first delinquency prevention experiment: A socio-historical review of the origins of the Cambridge-Somerville Youth Study’s research design. Journal of Experimental Criminology. DOI: 10.1007/s11292-018-9323-9.

Zane, S.N., Welsh, B.C., & Zimmerman, G.M. (2019). Criminal offending and mortality over the full life-course: A 70-year follow-up of the Cambridge-Somerville Youth Study. Journal of Quantitative Criminology. DOI: 10.1007/s10940-018-9399-4.

Tremblay, R.E., Welsh, B.C., & Sayre-McCord, G. (2019). Crime and the life-course, prevention, experiments, and truth seeking: Joan McCord’s pioneering contributions to criminology. Annual Review of Criminology, 1-20.

Welsh, B.C., Zane, S.N., & Rocque, M. (2017). Delinquency prevention for individual change: Richard Clarke Cabot and the making of the Cambridge-Somerville Youth Study. Journal of Criminal Justice, 52, 79-89.

Zane, S.N., Welsh, B.C., & Zimmerman, G.M. (2017). Examining the historical developments and contemporary relevance of the longitudinal-experimental design of the Cambridge-Somerville Youth Study: Utility for research on intergenerational transmission of offending. Adolescent Research Review, 2, 99-111.

Zane, S.N., Welsh, B.C., & Zimmerman, G.M. (2016). Examining the iatrogenic effects of the Cambridge-Somerville Youth Study: Existing explanations and new appraisals. British Journal of Criminology, 56, 141-160.

Welsh, B.C., & Zimmerman, G.M. (2015). Who cares about a delinquency prevention experiment of Boston boys born in the 1920s and 1930s? The need for long-term follow-ups in criminology. Criminal Behaviour and Mental Health, 25, 331-337.

Book Chapters

Welsh, B.C., Zane, S.N., & Wexler, A.B. (2018). The Cambridge-Somerville Youth Study and intergenerational transmission of criminal offending: Key findings and planning for the next generation. In V.I. Eichelsheim & S.G.A. van de Weijer (Eds.), Intergenerational Continuity of Criminal and Antisocial Behaviour: An International Overview of Studies (pp. 260-275). London: Routledge.

Welsh, B.C. (2017). The Cambridge-Somerville Youth Study: Some contributions to criminological theory, experimentation, and history. In C.C.J.H. Bijleveld & P.H. van der Laan (Eds.), Liber Amicorum Gerben Bruinsma (pp. 356-359). The Hague: Boom Criminologie.

Invited Presentations

Welsh, B.C. (2017). When juvenile diversion meets delinquency prevention. Discussant paper presented at Reducing Justice System Inequality conference, Princeton University, March 30-31, 2017.

Welsh, B.C. (2016). Who cares about a delinquency prevention experiment of Boston boys born in the 1920s and 1930s? Paper presented at School of Criminal Justice, State University of New York at Albany, Albany, NY, April 15, 2016.

Welsh, B.C. (2016). The Cambridge-Somerville Youth Study: Planning for research on the intergenerational transmission of offending. Paper presented at International Symposium on Multigenerational Datasets for Studying Intergenerational Transmission of (Delinquency and Antisocial) Behavior, Netherlands Institute for the Study of Crime and Law Enforcement, Amsterdam, The Netherlands, June 17-18, 2016.