Table 1.

Number of studies by subgroup analysis.

Subgroups	All Studies		Studies Reporting a Significant Negative Relationship between Fluoride Exposure and Cognition.
	n	Study Reference	n (%)	Study Reference
Study design
Longitudinal	6	[24,54,55,56,61,66]	3 (50)	[54,56,61]
Cross-sectional	40	[22,23,25,26,27,28,29,30,31,32,33,34,35,36,37,38,39,40,41,42,43,44,45,46,47,48,49,50,51,52,53,57,58,59,60,62,63,64,65,66,67]	34 (85)	[22,23,25,26,27,28,29,30,31,32,33,34,35,36,37,39,42,43,44,45,47,48,49,50,51,52,53,57,58,62,63,64,65,67]
Age group
≤8 yr	11	[23,24,28,34,54,55,56,58,60,61,62]	8 (72)	[23,28,34,54,56,58,61,62]
>8 yr	34	[22,25,26,27,29,30,31,32,33,35,36,37,38,39,40,41,42,43,44,45,46,47,48,49,50,51,52,53,59,63,64,65,66,67]	28 (82)	[22,25,26,27,29,30,31,32,33,35,36,37,39,42,43,44,45,47,48,49,50,51,52,53,63,64,65,67]
Not reported	1	[57]	1 (100)	[57]
Fluoride level
<2 mg/L	11	[26,35,40,52,54,55,59,60,61,62,66]	6 (54)	[26,35,52,54,61,62]
≥2 mg/L	26	[22,23,25,27,28,30,31,34,37,39,41,42,43,44,45,46,47,49,50,51,53,56,58,63,64,67]	24 (92)	[22,23,25,27,28,30,31,34,37,39,42,43,44,45,47,49,50,51,53,56,58,63,64,67]
Not reported	9	[24,29,32,33,36,38,48,57,65]	7 (77)	[29,32,33,36,48,57,65]
Study quality
Excellent	5	[25,40,55,60,61]	1 (20)	[61]
Good	7	[35,43,54,56,59,62,66]	5 (71)	[35,43,54,56,62]
Fair	14	[23,24,26,29,33,37,39,42,45,47,48,49,51,67]	13 (93)	[23,26,29,33,37,39,42,45,47,48,49,51,67]
Poor	20	[22,27,28,30,31,32,34,36,38,41,44,46,50,52,53,57,58,63,64,65]	17 (85)	[22,27,28,30,31,32,34,36,44,50,52,53,57,58,63,64,65]