In a critique of our study1 on the IQ of 9–12-year-old children in high- and low drinking water fluoride (F) areas in West Azerbaijan province, Iran, Dr Ken Perrott questioned whether possible confounding factors in the two villages, such as the rural status and parental educational levels, were adequately considered.2
Perrott’s comments on the rural status and the parental educational levels of the villages: Perrott noted that the only data presented were for F concentration and IQ and that no data were given to support two reassuring statements given by the authors: “The two rural areas studied had very similar populations, educational, economic, social, cultural, and general demographic characteristics but differed in the concentration of F in drinking water. Questionnaires were completed by the parents to measure potential confounding factors involving educational, economic, social cultural, and general demographic characteristics.” Perrott considered, despite these statements, that there was “absolutely no consideration of any other factors known to influence IQ” such as population size and parental educational levels.
Perrott stated that in the low-F area of Piranshahr (county), according to Wikipedia, Piranshahr city, Iran, “is one of the fastest-growing cities in Iran. The government’s mid-year estimate for 2013 puts Piranshahr’s population at 270,138 compared with the 2012 figure of 220,000. The city is forecast to have a population of approximately 320,000 by 2014 and 350,000 by 2015. Piranshahr has an educated population and its literacy rate is very high: of Piranshahr’s population over 28.60% (vs. a national average of 24%) hold a bachelor’s degree or higher; 945 (vs. 82% nationally) have a high school diploma or equivalent. In fact, Piranshahr has the highest percentage of college graduates of any city in the entire country.”
For the high-F region of Poldasht, Perrott observed that Poldasht city, Iran, was the capital of Poldasht county, West Azerbaijan province, Iran, and that at the 2006 census its population was 8,584, in 2,205 families. He commented that the city was smaller than Piranshahr and was situated “pretty much in the middle of nowhere” on the Iran/Armenian border. He recorded that he could not find any information on educational levels in Poldasht, pointed out that it was a small remote place, and thought that it was safe to infer that it was culturally and educationally less developed than Piranshahr.
Perrott quoted Dr Jonathan Broadbent as commenting that these towns (Piranshahr city and Poldasht city) were not comparable. Perrott stated that consequently neither would the satellite villages be comparable and that it
appeared that the authors may have indulged in a bit of confirmation bias through sample selection.
Our response to Dr Perrott’s critique: We note that despite the guidelines for authors for Fluoride stating that manuscripts need to be written as concisely as possible, it would have been helpful if we had provided more data in our initial paper and we apologize for this omission. However we do not accept Dr Perrott’s assessment that there was “absolutely no consideration of any other factors known to influence IQ” such as population size and parental educational levels. We now provide further information on the assessment of possible confounding factors in the two villages.