| Notes: | 1) | The figures are based on the total responses to the 1st through 4th surveys (total replies: 39,838). |
| 2) | The total includes the number of samples with "unknown" concerning sibling composition. |
| (1) | Sibling Composition
Approximately half of those who were an only child in the 1st survey had new brother(s) or sister(s) by the time of the 4th survey. Those who were the only child made up 48.8% of all survey subjects in the 1st survey (aged 6 months), but approximately half of them had new brother(s) or sister(s) by the time of the 4th survey (aged 42 months), resulting in the decreased rate of an only child to 24.1% (Figure 1). |
| Notes: | 1) | The figures are based on the total responses to the 1st through 4th surveys (total replies: 39,838). |
| 2) | The total includes the number of samples with "unknown" concerning sibling composition. |