Table 3 Important internal additive biases identified in the studies

Butte et al [12]

□ No information about immediate drop-outs; □ Recruitment not random.

□ 51 drop-outs, 81 exclusions from the analysis; □ Unclear whether drop-outs and exclusions differ from completers

□ Inappropriate adjustment; □ No stated justification for using confounders; □ Tanner stage assessed by self-report.

Deierlein et al [13]

□ Selections of clinics unclear.

□ ~12% losses to FU; □ ~30% exclusions from the analysis, who differ from completers.

□ Inappropriate adjustment; □ Self-reported pregravid BW; □ Assessment time unclear.

Iqbal et al [14]

□ Few inclusion, exclusion criteria&details of the original study cohorts; □ BL measures missing for 13% of the participants, unclear if they differ from those included.

□ Participation rate of 79%; □ 3 exclusions from the analysis.

□ Inappropriate adjustment; □ No stated justification for using confounders; □ Assessment of only leisure time PA; □ Measurement of confounders unclear.

Johnson et al [15]

□ 52% of children with incomplete datasets (little difference to children with complete datasets).

□ Inappropriate adjustment; □ Self-statement of parental BW and height; □ Time point of assessment of TV watching habits unclear.

McCaffrey et al [16]

□ Little information on the recruitment strategy, inclusion and exclusion criteria.

□ 58% of children were lost to FU (little difference to completers); □ 2 children were excluded from the analysis.

□ Inappropriate adjustment; □ Tanner stage assessed by self-report.

Savage et al [17]

□ No data describing the study sample.

□ 88% retention rate; □ Of the 68 women, dietary data were missing for 3, 9&18 women at years 2, 4&6.

□ The extracted model is unadjusted.