TABLE 3.
Sample characteristics (Percent or Mean/SD).
| Variable | Full sample (N = 18,445) | Only children (N = 8,161) | Non-only children (N = 10,284) |
| Mother–child relationship* | |||
| Not close (ref.) | 2.40 | 2.21 | 2.55 |
| Moderate | 24.21 | 21.76 | 26.15 |
| Close | 73.40 | 76.03 | 71.30 |
| Father–child relationship* | |||
| Not close (ref.) | 4.30 | 4.30 | 4.30 |
| Moderate | 33.28 | 31.26 | 34.88 |
| Close | 62.42 | 64.44 | 60.82 |
| Child’s gender* | |||
| Son (ref.) | 51.34 | 55.50 | 48.04 |
| Daughter | 48.66 | 44.50 | 51.96 |
| Grade | |||
| Grade 7 (ref.) | 52.55 | 52.09 | 52.91 |
| Grade 9 | 47.45 | 47.91 | 47.09 |
| Ethnicity* | |||
| Han (ref.) | 91.56 | 94.82 | 88.97 |
| Minority | 8.44 | 5.18 | 11.03 |
| Cognitive score (from −2.03 to 2.71)* | 0.02/0.86 | 0.23/0.85 | −0.15/0.83 |
| Academic performance (from 0 to 4)* | 2.07/1.12 | 2.16/1.12 | 1.99/1.12 |
| Boarding* | |||
| No (ref.) | 67.77 | 84.24 | 54.70 |
| Yes | 32.23 | 15.76 | 45.30 |
| Parental co-residence* | |||
| Both parents (ref.) | 77.40 | 82.51 | 73.34 |
| One parent | 12.36 | 12.14 | 12.53 |
| No parent | 10.24 | 5.34 | 14.13 |
| Marital quality of parents* | |||
| Not good (ref.) | 16.40 | 17.18 | 15.78 |
| Good | 83.60 | 82.82 | 84.22 |
| Family economic condition* | |||
| Low income (ref.) | 20.46 | 11.74 | 27.37 |
| Medium income | 73.46 | 80.84 | 67.61 |
| High income | 6.08 | 7.43 | 5.02 |
| Maternal education* | |||
| <Junior high (ref.) | 24.40 | 10.48 | 35.45 |
| =Junior high | 40.88 | 35.11 | 45.46 |
| > Junior high | 34.72 | 54.42 | 19.09 |
| Paternal education* | |||
| <Junior high (ref.) | 15.00 | 7.99 | 20.56 |
| =Junior high | 44.08 | 32.36 | 53.38 |
| >Junior high | 40.92 | 59.65 | 26.06 |
| Hukou type* | |||
| Rural (ref.) | 54.46 | 33.27 | 71.28 |
| Urban | 45.54 | 66.73 | 28.72 |
| Parental age at birth* | |||
| 18–24 | 23.93 | 25.99 | 22.29 |
| 25–29 | 35.19 | 42.87 | 29.08 |
| 30–34 | 12.29 | 10.40 | 13.78 |
| ≥35 | 4.00 | 2.59 | 5.11 |
| Missing | 24.61 | 18.15 | 29.74 |
*In the first column signals a significant difference between only and non-only children (p < 0.05). Significance of difference for each variable is determined by chi-squared test (for categorical variables) or t-test (for continuous variables).