Intervention effect of participation in the Northern Finland Birth Cohort 1986 study – Special reference to mental disorders and suicidal behavior

Abstract

Background

In the prospective follow-up studies participants are normally contacted during the follow-up. Even though the idea is not to intervene, the studies conducted during follow-up may affect the target population. Our hypotheses were that the participation to prospective Northern Finland Birth Cohort 1986 study (NFBC 1986) increases the use of mental health services and reduces the suicidal behavior due to intervention effect.

Methods

The NFBC 1986 covers the people born with expected date of birth between July 1985 and June 1986 in the former two northernmost provinces in Finland (N = 9396). The participants of the NFBC 1986 have been followed since antenatal time with follow-ups including clinical examinations. The comparison cohort comprises of all the people born in the same provinces in 1987 (N = 8959). Cumulative incidences were calculated to both cohorts and the difference was estimated with chi-square test. The relative risk (RR) with 95% confidence interval (CI) was calculated by sex.

Results

In males, the difference between NFBC 1986 and comparison cohort in mental disorders or in suicidal behavior were not detected. In females, decreased risk in the NFBC 1986 was found for any mental disorder (RR: 0.89 (CI: 0.81–0.98), p = 0.014) and in suicidal attempts (0.67 (0.49–0.92), p = 0.011).

Conclusions

Our hypothesis of increased mental disorders in the NFBC 1986 was not supported by the results. Second hypothesis was supported partly as female participants of the NFBC 1986 had less suicide attempts than comparison cohort. The intervention effect of participation in epidemiological follow-up study has been under-examined, and the results need to be replicated.