The study aimed to investigate the etiology of individual differences among twin-pairs age 80 and older, on a range of domains including health and functional capacity, cognitive functioning, psychological well-being, personality and personal control. 






OCTO-Twin Website

Start Year


End Year


General Design

Study Design Cohort
General Information on Follow Up (profile, frequency)

Participants were assessed up to 5 times at 2-year intervals providing up to 8 years of follow-up

Recruitment Target
  • Families
Number of Participants


Number of Participants with Biological Samples



Not Applicable
Don't Know
Possible Access to Data

Possible Access to Biosamples


Marker Paper

[McClearn, G. E., Johansson, B., Berg, S., Pedersen, N. L., Ahern, F., Petrill, S. A., et al. (1997). Substantial genetic influence on cognitive abilities in twins 80 or more years old. Science, 276, 1560-1563.]

PUBMED 9171059

Study Timeline

Each colour in the timeline graph below represents a separate Study Population, while each segment in the graph represents a separate Data Collection Event. Clicking on a segment gives more detailed information on a Data Collection Event.


OCTO-Twin - Population

Twin pairs were drawn from the Swedish population-based Twin Registry. At the first wave the twins had to be born 1913 or earlier and both partners in the pair had to accept participation. At the first wave 351 twin pairs (149 MZ and 202 like-sex DZ pairs) were investigated (average age 83.57 years; 67% of the sample were female). The two-year longitudinal follow-ups were conducted on all twins alive who agreed to participate, irrespective of twin status. The participation in the 2nd Wave was 235 pairs (568 individuals), in the 3rd wave 144 pairs (430 individuals), in the 4th wave 4 86 pairs (315 individuals), and at the last occasion (wave 5) 43 pairs (222 individuals participated. The initial OCTO-Twin sample was found to be similar to a representative sample of non-twins aged 80 and older (Simmons et al., 1997). Linkages are continuously performed to the Twin Registry/Census register and to the death register for vital status.

Sources of Recruitment

Specific Population
  • Other specific population : The Swedish population-based Twin Registry

Selection Criteria

Age Minimum age 79, Maximum age 98
Country Sweden

Sample Size

Number of Participants


Number of Participants with Biological Samples


Supplementary Information about Number of Participants

351 twin pairs, including 149 identical or monozygotic (MZ) pairs, and 202 same-sex fraternal or dizygotic (DZ) twin pairs

Data Collection Events

OCTO-Twin - wave 1


1991 (February)1994 (March)
OCTO-Twin - wave 2

First follow-up of participant. The number of...

1993 (May)1996 (May)
OCTO-Twin - wave 3

Second follow-up of participant. The number of...

1995 (April)1998 (May)
OCTO-Twin - wave 4

Third follow-up of participant. The number of...

1997 (April)2000 (May)
OCTO-Twin - wave 5

Fourth follow-up of participant. The number of...

1999 (December)2002 (March)

Variables classifications