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Table 1 Characteristics of the included studies

From: The effect of lead exposure on IQ test scores in children under 12 years: a systematic review and meta-analysis of case-control studies

Author Year Country Number of case group Number of control group Mean of IQ score in case group Standard deviation of case group Mean of IQ score in control group Standard deviation of control group Duration of the lead exposure (year) Cognitive function measurement Quality assessment (NOS)
Ibiwari C. Dike 2020 Nigeria 160 40 89.46 13.6 138.24 14.21 1.5 Raven’s standard progressive matrices Good
Nnenna Linda Nwobi 2019 Nigeria 169 140 86.9 11.6 91.5 14 4 Raven’s standard progressive matrices Fair
Todd A. Jusko 2008 USA 78 96 91.47 12.6 93.9 14.4 9 Wechsler Preschool and Primary Scale Good
Pamela J. Surkan 2007 USA 32 357 88.75 12.7 91.92 10.4 4 Wechsler Intelligence Scale for Children -Third Edition (WISC-III) Good
Katarzyna Kordas 2006 Mexico City 296 293 101.95 15.75 106.4 14.5 3 The testing battery Fair
Katarzyna Kordas 2004 Mexico City 291 298 103.13 15.06 106.3 14.6 3 Graphic Test of Reasoning (GTR) Good
Iman Al-Saleh 1 2001 Saudi Arabia 165 368 95.26 14.1 101.39 14.18 6 Beery VMI Saudi-based standard scores Good
Iman Al-Saleh 2 2001 Saudi Arabia 165 368 93.51 14.61 101.37 15.09 6 TONI Saudi-based scores and rank percentile Good