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Table 4 Quality assessment of studies included in the systematic review

From: Caesarean delivery and subsequent pregnancy interval: a systematic review and meta-analysis

Study Selection bias Exposure bias Outcome assessment bias Confounding factor bias* Analytical bias Attrition bias Overall likelihood of bias
Eijsink et al., 2008 [32] Moderate Low Low High (no adjustment for confounders reported, matched by maternal age and date of delivery) Low Minimal High
Collin et al., 2006 [10] Low Low Low Minimal (adjusted for age, parity, level of education, urban or rural residence and young age at first intercourse) Minimal Low Low
Smith et al., 2006 [18] Minimal Low Low Minimal (adjusted for marital status, deprivation, birth weight, infant sex, maternal age, maternal height and method of induction) Minimal Minimal Low
Murphy et al., 2002 [7] Low Low Low Minimal (adjusted for maternal and paternal age, co-habitation, oral contraceptive pill use, cigarette exposure, alcohol consumption, educational level, ethnicity, parity, change of partner, maternal BMI) Minimal Minimal Low
Zdeb et al., 1984 [33] Low Low Low Moderate (none reported). Matching by race, complications of pregnancy, maternal education and maternal age Moderate Low High
Tollånes et al., 2007 [16] Minimal Low Low Minimal (stratified by maternal age, level of education and infant survival). Sub-group analyses by low-risk group, pre-eclampsia and breech presentation Low Minimal Low
Tower et al., 2000 [16] Low Low Low Moderate (no adjustment for confounding). Matching by age and date of delivery Moderate Moderate High
Huttly et al., 1990 [34] Low Low Low Minimal (adjusted for income, age, education and parity) Moderate Moderate Low
Hemminki, 1987 [37] Low Low Low Moderate (no adjustment for confounders). Matching by year of birth, maternal age and infant sex Moderate Low High
LaSala et al., 1987 [35] Moderate Low Minimal Moderate (no adjustment for confounding reported). Matching by age and parity Moderate Moderate High
Hemminki et al., 1985 [36] Low Low Minimal Moderate (no adjustment reported). Matching by date of birth, mother’s age, race and marital status Moderate Minimal High
  1. Table Legend: *Assessment of confounding factor bias was done by evaluation of each study’s assessment of potential confounders by four methods: adjustment with regression, matching, assessment of potential confounders on univariate analyses that were found not to be significantly different between groups, and assessment of potential confounders on univariate analyses that were different between groups and not controlled for.