Objectives: To evaluate quality of sexual debut and first marriage data, measure trends and study the association of risky sexual behaviour in youth with adult risk behaviour.
Methods: Reports on age at first sex (AFS) and age at first marriage (AFM) from the Kisesa cohort study, 1994–2004, were evaluated for consistency and used to describe trends in median age-at-event and time spent single but sexually active in different birth cohorts. The association of these variables with marital stability and numbers of partners at later ages was explored using statistical regression techniques.
Results: AFS and AFM were inconsistently reported by 32% and 33% of respondents, respectively, but there was no general tendency to report lower or higher ages at a later report date. In 10-year birth cohorts born between 1950–9 and 1980–9, male median AFS declined from 18.1 to 17.0 years and female median AFM rose from 16.2 to 16.6 years. Young people of both sexes currently spend longer sexually active but unmarried than previously. Early marriage is statistically associated with remarriage and polygamy; longer time between sexual debut and marriage is associated with higher numbers of partners at later stages of life.
Conclusion: Inconsistent reporting of age-at-event introduces noise but does not bias estimates of population level indicators. Lengthening time spent single and sexually active suggests that men and women entering first marriage will have been exposed to increased numbers of non-marital partners. Successful youth interventions may also influence adult behaviour.
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Contributors: BZ: questionnaire design (round 4), data merging and editing (rounds 1–3), statistical analysis (young-old comparison) and drafting paper. RI: questionnaire design and data management (rounds 1–3), statistical analysis (data quality). AW: statistical analysis (data quality), drafting paper. MM: data merging and editing (round 4), statistical analysis (data quality). ES: development of methodology for data quality analysis, drafting paper. MU: fieldwork management, questionnaire design, director of cohort study. All co-authors reviewed draft versions of the papers, commented on and helped with editing and revisions.
Funding: The Kisesa cohort study has been financially supported by the Netherlands Ministry for Development Co-operation and the Global Fund for AIDS, TB and Malaria.
Competing interests: None.
Ethics approval: Ethical approval for the study was given in Tanzania by the Medical Research Co-ordinating Committee of the National Institute for Medical Research, Dar es Salaam and by the ethics committee of the London School of Hygiene and Tropical Medicine.