Table 1.
Individual-Level Risk Factors for Schizophreniaa
| Basic adjustmentc | Full individual-level adjustmentd | |||
|---|---|---|---|---|
| Individual-level risk factor | No of cases | Incidence Rateb | Incidence Rate Ratio (95% CI) | Incidence Rate Ratio (95% CI) |
| Residential changese | ||||
| None | 4013 | 2.73 | 1.00 (ref) | 1.00 (ref) |
| 1 or more | 1090 | 4.42 | 1.44 (1.38–1.51) | 1.26 (1.20–1.32) |
| Parental history of mental illness | ||||
| No | 4133 | 2.58 | 1.00 (ref) | 1.00 (ref) |
| Any | 970 | 8.23 | 3.11 (2.90–3.35) | 2.47 (2.29–2.65) |
| Paternal age (years) | ||||
| 12–19 | 98 | 4.21 | 1.53 (1.25–1.87) | 1.06 (0.85–1.32) |
| 20–24 | 1074 | 3.27 | 1.20 (1.11–1.29) | 1.06 (0.98–1.16) |
| 25–29 | 1873 | 2.69 | 1.00 (ref) | 1.00 (ref) |
| 30–34 | 1271 | 2.90 | 1.07 (1.00–1.14) | 1.09 (1.01–1.18) |
| 35–39 | 479 | 3.07 | 1.14 (1.03–1.25) | 1.10 (0.99–1.23) |
| 40 and older | 308 | 4.03 | 1.50 (1.33–1.69) | 1.29 (1.12–1.49) |
| Maternal age (years) | ||||
| 12–19 | 445 | 4.35 | 1.58 (1.42–1.75) | 1.27 (1.13–1.43) |
| 20–24 | 1747 | 2.99 | 1.11 (1.03–1.18) | 1.06 (0.99–1.14) |
| 25–29 | 1774 | 2.69 | 1.00 (ref) | 1.00 (ref) |
| 30–34 | 823 | 2.86 | 1.05 (0.97–1.14) | 0.99 (0.91–1.08) |
| 35–39 | 268 | 3.57 | 1.32 (1.14–1.51) | 1.11 (0.96–1.29) |
| 40 and older | 46 | 3.92 | 1.46 (1.07–1.96) | 1.06 (0.76–1.44) |
| Parental Charlson Comobidity | ||||
| Yes | 417 | 3.87 | 1.31 (1.19–1.44) | 1.04 (0.93–1.15) |
| No | 4686 | 2.91 | 1.00 (ref) | 1.00 (ref) |
| Parental imprisonment | ||||
| Yes | 395 | 6.41 | 2.17 (1.95–2.39) | 1.36 (1.22–1.52) |
| No | 4708 | 2.84 | 1.00 (ref) | 1.00 (ref) |
| Parental death | ||||
| Yes | 177 | 2.91 | 2.08 (1.79–2.40) | 1.23 (0.87–1.73) |
| No | 4926 | 6.18 | 1.00 (ref) | 1.00 (ref) |
| Parental income quartilef | ||||
| Q1 (lowest) | 547 | 4.83 | 1.90 (1.73–2.10) | 1.34 (1.19–1.50) |
| Q2 | 1060 | 3.27 | 1.30 (1.20–1.41) | 1.21 (1.11–1.31) |
| Q3 | 1500 | 2.80 | 1.11 (1.04–1.19) | 1.10 (1.02–1.18) |
| Q4 (highest) | 1851 | 2.56 | 1.00 (ref) | 1.00 (ref) |
| Parental educationf | ||||
| Primary school | 527 | 3.48 | 1.31 (1.18–1.44) | 0.96 (0.86–1.06) |
| High school/vocational training | 2854 | 2.88 | 1.06 (0.99–1.13) | 0.91 (0.84–0.97) |
| Short cycle higher education | 149 | 2.40 | 0.88 (0.74–1.04) | 0.84 (0.71–1.00) |
| Higher education | 1222 | 2.74 | 1.00 (ref) | 1.00 (ref) |
| Parental employment statusf | ||||
| Outside workforce | 169 | 9.60 | 3.34 (2.85–3.89) | 1.65 (1.39–1.95) |
| Unemployed | 252 | 7.07 | 2.52 (2.20–2.84) | 1.55 (1.35–1.78) |
| Employed | 4475 | 2.75 | 1.00 (ref) | 1.00 (ref) |
a Estimates were based on multilevel survival analyses, neighborhoods are 1885 novel data zones nested in Denmark’s 98 municipalities. The 579 039 people born in Denmark 1972–1981 were followed for development of schizophrenia. During the follow-up period from 1982 to 2016, a total of 5103 developed schizophrenia during the 17 191 889 person-years at risk
b The incidence rate measure the number of new people who developed schizophrenia per 10,000 person-years at risk.
c Estimates were adjusted for age and sex.
d Estimates were adjusted for age and sex and all other covariates.
e Incidence rate ratio for each residential change from 5th to 10th birthday.
f Parental income quartile was delineated as the maximum of maternal and paternal quartiles. Parental educational attainment was delineated as the parent with highest level of completed education. Parental employment status was delineated hierarchically as either parent employed, either parent not employed, and either parent outside workforce. Categories with missing parental socioeconomic position information are not shown.