Skip to content

Environmental Health Perspectives

Facebook Page EHP Twitter Feed Open Access icon  

Email this to someoneShare on FacebookTweet about this on TwitterShare on LinkedInShare on Google+Share on StumbleUpon

Developmental Fluoride Neurotoxicity: Choi et al. Respond

[do action=”authors”]Anna L. Choi1, Philippe Grandjean1, Guifan Sun2, Ying Zhang2[/do]

[do action=”affiliations”]1Harvard School of Public Health, Boston, Massachusetts, E-mail:; 2China Medical University, Shenyang, China[/do]

[do action=”citations”]Environ Health Perspect 121:a70–a70 (2013). [Online 1 March 2013]

[do action=”notes”]The author declares they have no actual or potential competing financial interests.[/do]

Sabour and Ghorbani’s comments about the reported mean difference in IQ (intelligence quotient) scores reported in our article (Choi et al. 2012) suggest a misunderstanding of the scale unit we used and the public health significance of even a small decrease in the average IQ associated with exposure. We appreciate this opportunity to clarify the factual information about the reported IQ measure.

The standardized weighted mean difference (SMD) in IQ score between exposed and reference populations was –0.45 (95% confidence interval: –0.56, –0.35) using a random-effects model (Choi et al. 2012). We used the SMD because the studies we included used different scales to measure the general intelligence. The SMD is a weighted mean difference standardized across studies, giving the average difference in standard deviations for the measure of that outcome. For commonly used IQ scores with a mean of 100 and an SD of 15, 0.45 SDs is equivalent to 6.75 points (rounded to 7 points). As research on other neurotoxicants has shown, a shift to the left of IQ distributions in a population will have substantial impacts, especially among those in the high and low ranges of the IQ distribution (Bellinger 2007).

Attached Files

PDF Version 


Bellinger BC. 2007. Interpretation of small effect sizes in occupational and environmental neurotoxicity: individual versus population risk. Neurotoxicology 28:245–251.

Choi AL, Sun G, Zhang Y, Grandjean P. 2012. Developmental fluoride neurotoxicity: a systematic review and meta-analysis. Environ Health Perspect 120:1362–1368.

WP-Backgrounds Lite by InoPlugs Web Design and Juwelier Schönmann 1010 Wien