Table 4. Potential confounding variables for each study group.
| Variable | Study group | ||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|
| ALSPAC | SCORM | REHS | IDFC | ||||||||
| Avail. | Uni. | Incl. | Avail. | Uni. | Incl. | Avail. | Uni. | Incl. | Avail. | Incl*. | |
| Sex | ✓ | ✓ | - | ✓ | ✓ | - | ✓ | ✓ | - | ✓ | ✓ |
| Ethnicity | NA | NA | - | ✓ | ✓ | ✓ | ✓ | ✓ | - | ✓ | ✓ |
| Parental myopia | ✓ | ✓ | ✓ | ✓ | ✓ | - | ✓ | ✓ | - | - | - |
| Time reading for pleasure | ✓ | ✓ | ✓ | ✓ | ✓ | - | ✓ | - | - | - | - |
| Time spent outdoors | ✓ | ✓ | - | ✓ | - | - | ✓ | ✓ | - | - | - |
| Socioeconomic status | ✓ | ✓ | ✓ | ✓ | ✓ | - | ✓ | - | - | ✓ | ✓ |
| Maternal age | ✓ | ✓ | ✓ | - | - | - | ✓ | ✓ | ✓ | - | - |
| Smoking during pregnancy | ✓ | ✓ | - | ✓ | - | - | ✓ | ✓ | - | - | - |
| Prematurity | ✓ | ✓ | - | - | - | - | ✓ | ✓ | - | - | - |
| Small for gestational age | ✓ | ✓ | - | - | - | - | ✓ | ✓ | - | - | - |
| Breast feeding | ✓ | - | - | ✓ | - | - | ✓ | - | - | - | - |
| IQ | ✓ | - | - | ✓ | - | - | ✓ | - | - | ✓ | ✓ |
| BMI | ✓ | - | - | ✓ | - | - | ✓ | - | - | ✓ | ✓ |
| Height | ✓ | - | - | ✓ | ✓ | - | ✓ | - | - | ✓ | ✓ |
| Season of birth | ✓ | - | - | ✓ | - | - | ✓ | - | - | ✓ | ✓ |
| Place of birth | NA | NA | - | ✓ | - | - | NA | NA | - | ✓ | ✓ |
Avail: tick indicates information on variable was available; Uni: tick indicates variable was tested in univariate analysis for association with birth order and myopia; Incl: tick indicates risk factor was associated with both myopia and birth order, and was included in the final logistic regression model. (*Note that for the IDFC sample, all available potential confounders were included in the final model).