"Costs and benefits of iodine supplementation for pregnant women in a mildly to moderately iodine-deficient population: a modelling analysis" (mirror; appendices), Monahan et al 2015

Background: Results from previous studies show that the cognitive ability of off spring might be irreversibly damaged as a result of their mother's mild iodine deficiency during pregnancy. A reduced intelligence quotient (IQ) score has broad economic and societal cost implications because intelligence affects wellbeing, income, and education outcomes. Although pregnancy and lactation lead to increased iodine needs, no UK recommendations for iodine supplementation have been issued to pregnant women. We aimed to investigate the cost-effectiveness of iodine supplementation versus no supplementation for pregnant women in a mildly to moderately iodine-deficient population for which a population- based iodine supplementation programme-for example, universal salt iodisation-did not exist.

Methods: We systematically searched MEDLINE, Embase, EconLit, and NHS EED for economic studies that linked IQ and income published in all languages until Aug 21, 2014. We took clinical data relating to iodine deficiency in pregnant women and the effect on IQ in their children aged 8-9 years from primary research. A decision tree was developed to compare the treatment strategies of iodine supplementation in tablet form with no iodine supplementation for pregnant women in the UK. Analyses were done from a health service perspective (analysis 1; taking direct health service costs into account) and societal perspective (analysis 2; taking education costs and the value of an IQ point itself into account), and presented in terms of cost (in sterling, relevant to 2013) per IQ point gained in the off spring. We made data-supported assumptions to complete these analyses, but used a conservative approach that limited the benefits of iodine supplementation and overestimated its potential harms.

Findings: Our systematic search identified 1361 published articles, of which eight were assessed to calculate the monetary value of an IQ point. A discounted lifetime value of an additional IQ point based on earnings was estimated to be £3297 (study estimates range from £1319 to £11 967) for the off spring cohort. Iodine supplementation was cost saving from both a health service perspective (saving £199 per pregnant woman [sensitivity analysis range -£42 to £229]) and societal perspective (saving £4476 per pregnant woman [sensitivity analysis range £540 to £4495]), with a net gain of 1·22 IQ points in each analysis. Base case results were robust to sensitivity analyses.

Interpretation: Iodine supplementation for pregnant women in the UK is potentially cost saving. This finding also has implications for the 1·88 billion people in the 32 countries with iodine deficiency worldwide. Valuation of IQ points should consider non-earnings benefits-eg, health benefits associated with a higher IQ not germane to earnings.

IQ estimates:

Our systematic search identified 1361 published articles, of which eight studies 47-54 passed quality criteria and were assessed to calculate the monetary value of an IQ point (appendix p 4). The quality criteria were as follows: an individual's IQ is used and is not a proxy; variables are clearly specified; IQ measure follows a conventional normal distribution with a mean of 100 and standard deviation of 15 or sufficient information is included in the study to allow the IQ measure's distribution to be converted into one (for cross study comparability); and the results reported in currency form have the applicable year stated. Most of the studies valued an IQ point on the basis of its effect on an individual's income (appendix p 3). The issue of differences in scaling of IQ tests hindered the comparability across studies. The value of an IQ point, derived from the systematic search and applied to the unborn cohort, comes from the lifetime earnings premium of an additional IQ point. This is calculated to be £3297 (study estimates range from £1319 to £11967; after adjustment with life tables).

All the details are in the Monahan et al 2015 appendices

One study looked at people's willingness to pay (WTP) for an additional IQ point. 4 Five studies used econometric regressions to determine the individuals IQ's effect on their subsequent income, 5-9 whereas two studies were cost benefit analysis on reducing lead exposure. 10,11 Only one of the studies included in the systematic literature search was not set in the USA. 5...In keeping with the conservative nature of the model, the relatively high earnings premium from IQ points from Schwartz 10 and Salkever 11 are excluded on the basis that the effect may be overstated.

The 8 studies are listed on pg8 of the appendix, Table 1:

• Fletcher J. "Friends or Family? Revisiting the Effects of High School Popularity on Adult Earnings". 2013. National Bureau of Economic Research Working Papers: 19232
• Lutter RW. "Valuing children's health: A reassessment of the benefits of lower lead levels". AEI-Brookings Joint Center Working Paper No. 00-02. 2000.
• Mueller G, Plug E. "Estimating the Effect of Personality on Male and Female Earnings". Ind Lab Relat Rev. 2006;60(1):3-22.
• Salkever DS. "Updated estimates of earnings benefits from reduced exposure of children to environmental lead". Environ Res. 1995;70(1):1-6.
• Schwartz J. "Societal benefits of reducing lead exposure". Environ Res. 1994;66(1):105-24.
• de Wolff P, van Slijpe ARD. "The Relation Between Income, Intelligence, Education and Social Background". Europ Econ Rev. 1973;4(3):235-64.
• Zax JS, Rees DI. IQ, "Academic Performance, Environment, and Earnings". Rev Econ Stat. 2002;84(4):600-16
• Zagorsky JL. "Do you have to be smart to be rich? The impact of IQ on wealth, income and financial distress". Intelligence. 2007;35(5):489-501.

(Note that by including covariates that are obviously caused by IQ rather than independent, and excluding any attempt at measuring the many positive externalities of greater intelligence, these numbers can usually be considered substantial underestimates of country-wide benefits.)