Table 2.
Univariable analysis of categorical early life variables and hand preference. OR refers to the odds ratio, CI to the confidence interval.
| TRAIT | N | P | Frequency of left-hand preference | Notes | OR for right-hand preference (95% CI) |
|---|---|---|---|---|---|
| Sex (male) | 421,667 | 2.0E-113 | females = 8.6%, males = 10.6%, | 46% males | 0.79 (0.77–0.80) |
| Part of multiple birth | 414,560 | 5.9E-08 | single = 9.5%, multiple = 11.2% | 2.2% of participants are from multiple birth | 0.83 (0.78–0.89) |
| Maternal smoking | 363,866 | 0.102 | non-smoking = 9.4%; smoking = 9.6% | 29% of mothers smoked around pregnancy | 0.99 (0.99–1.00) |
| Breastfeeding | 322,576 | 1.55E-26 | breastfed = 9.1%, not breastfed = 10.3% | 72% of participants were breastfed | 1.15 (1.12–1.18) |
| Country of origin | 420,939 | 1.4E-150 | Lowest frequency left-handers born outside UK, highest in England | ||
| England | 322,287 | 10.1% | |||
| N. Ireland | 2,899 | 8.8% | |||
| Scotland | 34,424 | 8.1% | |||
| Wales | 18,370 | 7.3% | |||
| Rep. of Ireland | 4,801 | 7.3% | |||
| Elsewhere | 38,158 | 6.8% |