Testing anonymous link procedures for follow-up of adolescents in a school-based trial: the EU-DAP pilot study.
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.
Galanti
M Rosaria
MR
Stockholm Center for Public Health/Tobacco Prevention, Box 17533 118 91 Stockholm, Sweden. rosaria.galanti@sll.se
Siliquini
Roberta
R
Cuomo
Luca
L
Melero
Juan Carlos
JC
Panella
Massimiliano
M
Faggiano
Fabrizio
F
D000293:Adolescent; D003266:Continuity of Patient Care; D003625:Data Collection; D005060:Europe; D005062:European Union; D005240:Feasibility Studies; D005260:Female; D005500:Follow-Up Studies; D005568:Forms and Records Control / Q000379:methods*; D019538:Health Care Surveys / Q000379:methods*; D006293:Health Promotion / Q000458:organization & administration*; D006801:Humans; D008297:Male; D010865:Pilot Projects; D015397:Program Evaluation; D012572:School Health Services / Q000458:organization & administration*; D019966:Substance-Related Disorders / Q000517:prevention & control*