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Table 2 Quality assessment of included studies

From: Physical activity is associated with reduced risk of esophageal cancer, particularly esophageal adenocarcinoma: a systematic review and meta-analysis

  Bias in study design Bias in instrument to measure physical activity Bias in accounting for confounding variables Overall quality of study
Cohort studies
Huerta [15] Low Low Low High
Leitzmann [16] Low Low Low High
Wannamethee [23] Low Low Low High
Yun [24] Low Low Low High
Case–control Studies
Balbuena [26] High High High Low
Brownson [25] High High Low Low
Etemadi [27] High High High Low
Parent [13] Low High Low Low
Vigen [14] Low High Low Low
  1. Briefly, we used a three-item checklist to identify whether studies were at low or high risk of bias, based on: (a) study design – low risk of bias if cohort or population-based case–control studies, and high risk of bias if hospital-based case–control or exclusively cancer registry-based; (b) instrument used to measure physical activity – low risk of bias if instrument valid and reliable as shown in index study or related study, and high risk of bias if not reported; (c) key variables adjusted or accounted for: if a study adjusted, matched or accounted for the potential confounding effect of age, sex and obesity in their analysis, then those studies were considered to be at low risk of bias, otherwise they were considered to be at high risk of bias. Overall, if a study was deemed to be at low-risk of bias across all these domains, then it was considered a high-quality study, otherwise it was considered a low-quality study.