Table 6 Risk of bias table

Incomplete outcome data (attrition bias)

Gilliland et al., 2003[45]; Gold et al., 2003[46]; Mannino et al., 2006[48]

Unclear risk

Number of participants lost to follow-up not reported

Mamun et al., 2007[47]

High risk

46.5% of original cohort lost to follow-up by age 5 years; 59.6% of original cohort has incomplete data at either age 5 years or 14 years and was excluded from analysis

Zhang et al., 2010[49]

Low risk

89.6% of original cohort sampled at 6 year visit; 82.4% of original cohort sampled at 8 year visit

Ho et al., 2011[50]

Unclear risk

82% of selected original cohort with complete data at 12 month follow-up

Ascertainment bias

Gilliland et al., 2003[45]; Gold et al., 2003[46]; Mamun et al., 2007[47]; Mannino et al., 2006[48]; Zhang et al., 2010[49]; Ho et al., 2011[50]

Unclear risk

Unclear if children who were overweight or obese were more likely to be diagnosed with asthma

Differential misclassification of exposure bias

Mannino et al., 2006[48]

High risk

Only 69% of height and 61% of the weights were measured