1. Register-based research in the Nordic countries
Mika Gissler
Nordic School of Public Health, Gothenburg, Sweden &
THL National Institute for Health and Welfare, Helsinki, Finland

2. Why good possibilities to register-based studies?
Traditions: population statistics have been collected more than 250 years and health statistics more than 150 years in the Nordic countries.
First real registers were started in the s, when improved computers were available: health care personnel, cancer register.
Personal identification numbers since 1960s.
Several data quality studies have shown the high quality of routinely collected registers.
Data protection allows research use of register data.

3. Important registers in the Nordic countries
Cancer register s
Registers on infectious diseases 1950s
Hospital discharge registers 1960s
Cause-of-death registers 1960s
Birth and malformation registers 1960s
Register-based Census s
Health care quality registers 1990s
Prescription registers s
Hospital outpatient registers 1990s

4. Unique registers and data in the Nordic countries
IVF (in vitro fertilization) register, Denmark
Register on induced abortions and sterilisations, Finland
Register on visual impairments, Finland
Register on breast and cervical cancer screening, Finland
Multiple generation register, Sweden
Multiple generation studies in the Norwegian Medical Birth Register
Biobanks in all Nordic countries + possibilities to link them to other registers.

5. Important registers for studies in psychiatry and mental health
Hospital discharge registers 1960s
Cause-of-death registers s
Pension Registers s
Register-based Census s
Prescription registers s
Hospital outpatient registers 1990s

6. Examples of register-based studies in psychiatry and mental health
Cross-sectional studies
Trends
Longitudinal studies
Combination of data from different sources:
Medical records
Questionnaires
Biobank material

7. Example 1: Life expectancy among psychiatric patients
Registers:
THL: Hospital Discharge Register
Finnish Centre of Pension: Pension Register
Statistics Finland: Cause-of-Death Register
Data:
The data included persons aged 15 years or more
persons with dementia and with intellectual disability were excluded
Life expectancy at 15 years and for ages years were calculated separately by using Wiesler's method.

8. Life expectancy increased

9. Conclusions
Life expectancy at 15 years has increased among Finnish population with hospital discharge or pension due to mental disorders between 1981 and 2003:
Finland: +3.5 years, psychiatric patients +5.8 years
F30-39: +10 years, F40-49: +8 years, F20-29: +6 years, but
F10-19: -0.6 years
Risk for death
diseases and medical conditions 2-fold
external causes and poisoning 6-fold
Similar results from other Nordic countries.

10. Example 2: Maternal smoking and children’s F-diagnoses
Registers:
THL: Medical Birth Register
THL: Hospital Discharge Register
Social Insurance Institute: Reimbursed psychotropic medicine
Statistics Finland: Cause-of-Death registers
Data:
Children born in , excluding perinatal deaths, multiples, and children with major congenital anomalies
Final study population: 175 869 children (94.4%)

11. Risk for adverse psychiatric outcomes by maternal smoking
Adjusted by maternal age, parity, sex, gestational age, birth weight, 5 minute Apgar score and
maternal psychiatric diagnosis before birth.

12. Conclusions
Children exposed to maternal smoking has an increased risk for receiving a F-diagnosis in inpatient or outpatient care in childhood and adolescent.
The increased risk can be observed for all diagnosis excluding schizophrenia and anorexia.
Register studies cannot confirm the real effect of smoking.
However, a recent local study in Turku has shown that prenatal smoking exposure is associated with smaller regional brain volumes in preterm infants (Ekblad et al., J Pediatrics 2009).

13. Example 3: Use of psychotropic drugs and pregnancy outcomes
Registers:
The ‘Drug and Pregnancy’ -database , to be annually completed 2007 onwards
Data:
All births in the Medical Birth Register
All induced abortions in the Abortion Register
All congenital anomalies in the Malformation Register
Use of prescribed & reimbursed drugs (Social Insurance Institution)
3 months before pregnancy
during pregnancy
3 months after pregnancy

14. The use of psychotropic medicine before the pregnancy starts
The Drug and Pregnancy -database :
Total births and induced abortions
Excluded: induced abortions due to fetal reasons
Separate analysis: first pregnancies
All drug purchases 3 months before pregnancy were used as a proxy measure of mental health disorders.

15. Conclusions
Measured by the use of psychotropic medicine, women’s pre-existing mental health status is worse for women having an induced abortion than for women giving a birth.
All pregnancies: Adjusted OR 1.94 (95% CI )
First pregnancies: Adjusted OR 1.56 (95% CI )
Highest risk for women using hypnotics and sedatives, antipsychotics and antidepressants.
This essential confounding factor should not be neglected when investigating the occurrence of pregnancy-related mental health problems.

16. Example 4: Mothers’ and children’s long-term follow-up after substance abuse during pregnancy
Basic data:
524 women followed-up prenatally at special out-patient clinics and a control group of 1792 women matched for maternal age, parity, time and place of delivery.
Registers:
THL: Medical Birth Register, Hospital Discharge Register, Child Welfare Register
Statistics Finland: Cause-of-Death Register
Social Insurance Institution: Information on prescribed medicine, social benefits, pensions and rehabilitations

17. Mothers’ outcome, % Death 8.0 0.2 ***
Cases Controls
Death ***
F-diagnosis, inpatient ***
F-diagnosis, outpatient ***
Intoxication care ***
Pensions, any cause ***
Rehabilitation, any cause ***
Special reimbursement ***
Psychosis ***
Drug reimbursement N ***
Drug reimbursement N ***

18. Children’s outcome, % Death 1.4 1.0 NS
Cases Controls
Death NS
F-diagnosis, inpatient ***
F-diagnosis, outpatient ***
Care benefit for sick child ***
Rehabilitation, any cause ***
Special reimbursement NS
Drug reimbursement N **
Drug reimbursement N ***
Child taken into custody ***

19. Conclusions
Combination of medical records and registers was feasible, even though it was difficult to get all the necessary permissions.
Women with substance abuse displayed significant long-term abuse-related morbidity and mortality, rehabilitation, early retirement, and use of prescribed medicine.
Also their children had increased morbidity, rehabilitation, and use of prescribed medicine, and almost half of them were taken into custody.

20. Why register research? Easy to form data:
cross-sectional studies
longitudinal studies (history, follow-up)
Easy to repeat the same study.
No limitations for sample size (rare cases --- total population).
Population-based studies feasible.
No need to contact patients.
Follow-up relatively easy.
No participation bias nor research bias.
No reporting bias.

21. Problems related to register research
The data is unavailable
primary health care, diseases and conditions not requiring a contact to health care system, self-rated health, opinions, experiences,...
Data protection: are such studies possible in general?
Ethically controversial topics:
abortion, miscarriage, infertility, malformations, psychiatric disorders, family studies, contact to relatives of a death patient, genetics…
High data costs: Statistical offices, Central Population Register
Data overload syndrome
Too much data, too little time…?
Fishing:
Easy to find statistically significant results, if the data is large.

22. Finally
Register-based studies seems to be feasible, e.g. for cross-sectional, longitudinal and trend studies
Combination of data from other registers and from other sources, such as medical records, questionnaires and even biobank material is possible.
Data protection questions have not been an issue, at least until now.
The lack of information from primary health care will be solved after the national electronic patient journal system is in use.

23. Promotion of register research
Denmark: National Centre for Register-based Research, Århus Universitet
Finland: Finnish Information Centre for Register Research
Norway: Special issue on register-based research in Norsk Epidemiologi 14 (1): 2004.
Sweden: Grants for register-based research by the National Board of Welfare and Health (Social-styrelsen)