Table 5.
Cross-twin logistic regression to examine the heritability of ideation independent of the heritability of depression
| Predicting Twin 1 ideation from Twin 2 ideation | |||||||
|---|---|---|---|---|---|---|---|
| 1. Controlling for age, sex and ethnicity OR (95% CI) | 2. As Model 1, plus controlling for Twin 2 depression OR (95% CI) | 3. As Model 1, plus controlling for Twin 2 alcohol abuse OR (95% CI) | 4. As Model 1, plus controlling for Twin 2 depression and alcohol abuse OR (95% CI) | Effect of zygosity in Model 2 | Effect of zygosity in Model 3 | Effect of zygosity in Model 4 | |
| All | 3.80 (2.90–4.99) | 3.52 (2.67–4.64) | 3.73 (2.88–4.97) | 3.51 (2.65–4.63) | Z = 2.80, p = 0.005 | Z = 2.66, p = 0.008 | Z = 2.73, p = 0.006 |
| MZ | 5.68 (3.72–8.69) | 5.24 (3.41–8.05) | 5.63 (3.68–8.61) | 5.20 (3.39–7.99) | |||
| DZ (incl DZOS) | 2.71 (1.88–3.91) | 2.51 (1.72–3.65) | 2.68 (1.86–3.87) | 2.49 (1.71–3.62) | |||
| Men (excl DZOS) | 4.19 (2.26–7.79) | 3.84 (2.02–7.31) | 4.06 (2.17–7.59) | 3.76 (1.96–7.19) | Z = 2.58, p = 0.01 | Z = 2.46, p = 0.014 | Z = 2.57, p = 0.010 |
| MZM | 8.07 (3.59–18.11) | 7.17 (3.16–16.29) | 7.86 (3.48–17.74) | 7.09 (3.10–16.23) | |||
| DZM | 1.34 (0.42–4.27) | 1.27 (0.38–4.22) | 1.24 (0.37–4.11) | 1.19 (0.35–4.09) | |||
| Women (excl DZOS) | 4.22 (2.89–6.18) | 3.94 (2.68–5.81) | 4.22 (2.89–6.18) | 3.94 (2.68–5.81) | Z = 1.09, p = 0.28 | Z = 1.04, p = 0.299 | Z = 1.09, p = 0.277 |
| MZF | 4.96 (3.04–8.08) | 4.64 (2.84–7.57) | 4.96 (3.05–8.08) | 4.64 (2.84–7.57) | |||
| DZF | 3.16 (1.70–5.88) | 2.95 (1.55–5.62) | 3.16 (1.70–5.88) | 2.95 (1.55–5.62) | |||
| DZ OS | 2.74 (1.63–4.60) | 2.54 (1.50–4.30) | |||||
DZOS, DZ opposite sex pairs.
Models 3 and 4 have been included for women for completeness; though as we note earlier, alcohol abuse is very rare in women in this population so these models are largely unchanged after accounting for female alcohol abuse.