Table 1. Studies included in the meta-analysis.
| Study | Source | Country | Type | N indv | N pair | Agea | Datab | % Female | Cognitive Domain (# tests) |
|---|---|---|---|---|---|---|---|---|---|
| Central Valley of Costa Rica | Greenwood et al., 2011 | Costa Rica | Family | 253 | NAc | 73.3 (12.7) | H | 65 | Executive function (3) General memory (4) Verbal (2) |
| Diabetes Heart Study | Cox et al., 2014 | U.S. | Family | 550 | NA | 67.3 (8.8) | H | 55 | Executive function (3) General memory (1) Speed (1) |
| Genetics of Brain Structure and Function | Glahn et al., 2013 | U.S. | Family | 1129 | NA | 44.2 (14.0) | H | 62 | Executive function (3) General memory (6) Speed (3) Verbal (1) Working memory (7) |
| German Observational Study of Adult Twins | Neubauer et al., 2000 | Germany | Twin | 600 | 169 MZ 131 DZ |
34.3 (13.0) | H | 78 | Executive function (4) Spatial (2) Speed (1) Verbal (3) Working memory (2) |
| Italian Twin Registry | Giubelei et al., 2008 | Italy | Twin | 186 | 35 MZ 58 DZ |
67.6 (4.7) | H | 61 | Executive function (3) General memory (1) Spatial (1) |
| Keio Twin Study | Ando et al., 2001 | Japan | Twin | 472 | 142 MZ 94 DZ |
19.9 (3.5) | TC | 67 | Executive function (2) General memory (2) Spatial (1) Verbal (1) |
| Kinki University Adult Twin Registry | Hayakawa et al., 1992 | Japan | Female twins | 66 | 30 MZ 3 DZ |
50-78 | TC | 100 | Spatial (1) Speed (1) Working memory (1) |
| Male twins | 128 | 46 MZ 18 DZ |
50-78 | TC | 0 | Spatial (1) Speed (1) Working memory (1) |
|||
| Longitudinal Study of Aging Danish Twins | McGue et al., 2001 | Denmark | Twin | 806 | 168 MZ 235 DZ |
80.0 (4.0) | H | 70 | General memory (1) Verbal (1) Working memory (1) |
| Minnesota Study of Twins Reared Apart | Bouchard et al., 1990 | U.S. | Twin | 112 | 56 MZA | 41.0 (12.0) | TC | NRd | Verbal (1) |
| Minnesota Twin Study of Adult Development and Aging | Finkel & McGue, 1993 | U.S. | Twin | 320 | 93 MZ 67 DZ |
67.0 (6.7) | H | 50 | General memory (4) Speed (1) |
| Finkel et al., 1995 | Younger Twin | 140 | 41 MZ 21 DZ |
38.9 (4.4) | H | 75 | Spatial (1) Speed (1) Verbal (1) Working memory (1) |
||
| Middle Aged Twin | 176 | 50 MZ 30 DZ |
60.1 (3.9) | H | 56 | Spatial (1) Speed (1) Verbal (1) Working memory (1) |
|||
| Older Twin | 66 | 41 MZ 40 DZ |
69.3 (5.8) | H | 54 | Spatial (1) Speed (1) Verbal (1) Working memory (1) |
|||
| Finkel & McGue, 1998 | Younger Twin | 294 | 86 MZ 61 DZ |
43.3 (8.3) | H | 68 | General memory (3) Verbal (1) |
||
| Older Twin | 388 | 115 MZ 79 DZ |
69.8 (10.5) | H | 54 | General memory (3) Verbal (1) |
|||
| Finkel & McGue, 2007 | Twin | 738 | 185 MZ 131 DZ |
58.7 (NR) | H | 60 | Speed (2) | ||
| National Heart Lung Blood Institute | Swan et al., 1990 | U.S. | Twin | 524 | 134 MZ 133 DZ |
63 (NR) | H | 0 | Speed (1) |
| Swan et al., 1999 | Twin | 366 | 94 MZ 89 DZ |
71.8 (2.9) | H | 0 | General memory (1) Verbal (3) |
||
| Netherlands Twin Registry | Posthuma et al., 2001 | The Netherlands | Twin-family | 688 | 102 MZ 131 DZ |
37 (NR) | H | 56 | Speed (1) Verbal (1) |
| Posthuma et al., 2002 | Twin-family | 135 | 24 MZ 31 DZ |
30.0 (9.0) | H | 45 | Working memory (1) | ||
| Norwegian Twin Panel | Tambs et al., 1994 | Norway | Twin | 160 | 40 MZ 40 DZ |
41.0 (8.1) | H | 53 | Spatial (4) Speed (1) Verbal (5) Working memory (2) |
| Older Australian Twin Study | Lee et al., 2012 | Australia | Twin | 472 | 117 MZ 98 DZ |
71.0 (5.2) | H | 66 | Executive function (3) Working memory (1) |
| OCTO-Twin | McClearn et al., 1997 | Sweden | Twin | 388 | 90 MZ 104 MZ |
82.3 (NR) | H | 64 | General memory (1) Spatial (1) Speed (1) Verbal (1) |
| Johansson et al., 1999 | Twin | 564 | 125 MZ 157 DZ |
83.3 (3.1) | H | 64 | General memory (4) Working memory (2) |
||
| Russian Twin Study | Malykh et al., 2005 | Russia | Twin | 160 | 40 MZ 40 DZ |
21.7 (3.3) | H | 50 | Verbal (1) |
| Swedish Adoption Twin Study of Aging | Pedersen et al., 1992 | Sweden | Twin | 645 | 113 MZ 189 DZ |
65.6 (8.4) | H | 60 | General memory (3) Spatial (3) Speed (3) Verbal (3) Working memory (2) |
| Swedish Adoption Twin Study of Aging | Finkel et al., 1995 | Younger Twin | 102 | 21 MZ 30 DZ |
41.1 (5.9) | H | 47 | Spatial (1) Speed (1) Verbal (1) Working memory (1) |
|
| Middle-Aged Twin | 146 | 35 MZ 29 DZ |
58.8 (4.3) | H | 49 | Spatial (1) Speed (1) Verbal (1) Working memory (1) |
|||
| Older Twin | 164 | 30 MZ 51 DZ |
71.6 (4.8) | H | 66 | Spatial (1) Speed (1) Verbal (1) Working memory (1) |
|||
| Finkel & Pedersen, 2014 | Twin | 241 | 64 MZ 96 DZ |
66.5 (7.8) | H | 61 | Speed (2) | ||
| TwinsUK | Singer et al., 2006 | U.K. | Twin | 556 | 108 MZ 170 DZ |
56.0 (11.0) | H | 100 | General memory (1) Speed (2) Verbal (1) Working memory (1) |
| Vietnam Era Twin Study of Aging | Kremen et al., 2005 | U.S. | Twin | 690 | 179 MZ 169 DZ |
47.9 (3.3) | H | 0 | Verbal (1) |
| Kremen et al., 2014 | Twin | 1237 | 349 MZ 265 (DZ) |
55.4 (2.5) | H | 0 | General memory (6) |
a
Mean age (standard deviation) if reported, otherwise age range
b
Type of data reported: H = heritability estimate, TC = twin correlations
c
NA indicates “not applicable”
d
NR indicates “not reported”