Table 3.

Important internal additive biases identified in the studies

Study	Selection bias	Attrition bias	Confounding bias
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.

BW = body weight; BL = baseline; FU = follow-up; PA = physical activity.