Testing anonymous link procedures for follow-up of adolescents in a school-based trial: the EU-DAP pilot study

Prev Med. 2007 Feb;44(2):174-7. doi: 10.1016/j.ypmed.2006.07.019. Epub 2006 Sep 18.


Objective: To study the feasibility of an anonymous coding procedure linking longitudinal information in a multi-center trial of substance abuse prevention among adolescents.

Methods: A school-based survey with re-test procedure was conducted among 485 students (mean age 13.8 years) from three countries at four study centers in order to study accuracy and repeatability of a self-generated anonymous code.

Results: Errors affected 18% of codes and 3% of all digits required for the code generation, with highest figures for two of the seven generation items. Sixty-one percent of the codes generated at the test were repeated identically at the re-test. Seventy-six percent of the codes could be linked excluding the 2 digits with the highest error rate in code generation, while 92% were linked using the best combination of the remaining seven or six digits. There was substantial variation between the centers in the results.

Conclusions: Self-generation of anonymous codes is a feasible, but not a very efficient procedure to link longitudinal data among adolescents. Easy derivation and iterative matching procedures are crucial for achieving high efficiency of this type of anonymous linkage.

Publication types

  • Multicenter Study
  • Research Support, Non-U.S. Gov't
  • Validation Study

MeSH terms

  • Adolescent
  • Continuity of Patient Care
  • Data Collection
  • Europe
  • European Union
  • Feasibility Studies
  • Female
  • Follow-Up Studies*
  • Forms and Records Control / methods*
  • Health Care Surveys / methods*
  • Health Promotion / organization & administration*
  • Humans
  • Male
  • Pilot Projects
  • Program Evaluation
  • School Health Services / organization & administration*
  • Substance-Related Disorders / prevention & control*