The 1924 Iodine-Cognition Anomaly – A 90-Year Data Failure

In May 1943, a War Department training manual gave a strange instruction to clerical staff. Clerks were told to take the Army General Classification Test scores and punch them into columns 76 to 78 of the Hollerith card. These three columns were not empty. They were the designated field for a recruit’s body weight.

For the rest of the war, the military systematically overwrote the physical record of every soldier with his cognitive score. This clerical shortcut erased the one piece of evidence that might have connected a 15-point national intelligence jump to a spoonful of salt. The military held both halves of a public health miracle in two different offices and never once laid them side by side. Nobody noticed the connection until 2013.

The Goitre Belt on a Map

The Surgeon General’s Office (SGO) knew exactly where the problem was in 1920. Their definitive report, Defects Found in Drafted Men, was authored by Albert Love and Charles Davenport. It was a massive statistical exercise that mapped the country into 151 geographic sections. The data showed that goitre was not a national average but a highly localised phenomenon. Idaho had a rate of 27 per 1,000 men. Florida had a rate of just 0.25.

Military doctors viewed these swollen thyroid glands through a purely physical lens. A man with a severe goitre could not button his tunic or breathe well while carrying a heavy pack under load. In Houghton County, Michigan, a draft board physician named Simon Levin recorded that nearly 30 per cent of his 583 registrants were rejected for thyroid-related issues in 1919. The brain was not part of the conversation.

These volumes were archived as a static snapshot of the First World War. Because the SGO saw the problem as a physical disqualification rather than a neurological one, the records were frozen. The medical branch closed the file on these geographic defects just as the intervention that would fix them was beginning in the civilian world.

A Spoonful of Salt, 1 May 1924

Records show the fix started in June 1922 at a symposium of the Michigan State Medical Society (MSMS). Dr David Murray Cowie led the charge, forming an Iodized Salt Committee to combat the ‘goitre belt’ at the state level. They faced a choice between passing slow-moving laws or working with the private sector.

On 12 March 1924, the MSMS Executive Council chose the faster route and endorsed commercial distribution.

According to committee records, iodised salt arrived on Michigan grocery shelves on 1 May 1924. By that autumn, the Morton Salt Company rolled the product out nationally. This date marks a clean line in the historical record. Every child born after May 1924 in a high-goitre region was receiving a biochemical intervention that their older siblings had missed. It was a massive, uncoordinated human trial.

Because the rollout was managed by companies like Dow Chemical and Morton Salt, no public health agency held the distribution ledgers. The MSMS had fixed a neck problem and felt no mandate to track cognitive outcomes. The government had no longitudinal tracking process in place for how well these children could think.

Two Wars, Two Offices, One Recruit

By 1940, the babies born during the 1924 salt rollout were reaching military age. The Adjutant General’s Office (AGO) established the Personnel Research Section (PRS) to handle them. Their job was to build the Army General Classification Test (AGCT), which was cleared for use on 9 August 1940. The AGO wanted to measure ‘learning ability’ to sort nine million recruits into technical roles.

The silo was spatial as much as it was intellectual.

A recruit at an induction centre walked through a physical station for his medical exam and a cognitive station for his test. The SGO doctors were looking for ‘physical viability’ while the AGO psychologists were looking for ‘trainability’. The two departments were looking at the same human asset through two different keyholes.

The psychologists were focused on standardising their new test and overcoming the limits of rural schooling. They did not consult the Surgeon General’s 1920 maps because they saw low scores as a social or educational issue, not a nutritional one. There are no surviving liaison memoranda between these two offices from 1940 to 1945. The records lived in parallel channels that never crossed. A high score from a recruit in a formerly high-goitre county was seen as a personal success or the result of a better schoolhouse.

Columns 76 to 78

The most striking moment of data destruction happened on 1 May 1943. The War Department issued Training Manual TM-12-305. It was a technical guide for the clerks operating the punch card machines. The manual explicitly told them to input AGCT scores into columns 76 to 78. These columns were already designated for the recruit’s body weight.

The decision was a matter of hardware limits. An IBM Hollerith card only has 80 columns. Under the pressure of a two-front war, the military needed to sort technicians faster than it needed to track biometric trends. They chose to keep the intelligence data and literally punch it through the physical data. The weight of nine million men vanished to make room for their test scores.

This act of administrative pragmatism was done while the military publicly claimed its personnel systems were the height of scientific rigour. They believed ‘unaided human judgement’ was unreliable, yet they were physically destroying the data needed for a real scientific review. The physical medium itself, paper cards stored in separate buildings, enforced the silo. No document in the research pack identifies which official authorised TM-12-305. We do not know if the logistics chain at the AGO even asked the Surgeon General for permission to erase the weight records.

Tuddenham’s 1948 Full Stop

In 1948, a researcher named R.D. Tuddenham published a paper in American Psychologist. He compared the WWI Army Alpha scores to the WWII AGCT results and found a massive jump. Average intelligence had risen by roughly 15 points, or one full standard deviation. It was the first major documentation of what would later be called the Flynn Effect.

Tuddenham’s conclusion was simple… ‘more and better education’. He found a 0.75 correlation between years of schooling and test scores, which seemed to close the case.

The educational narrative stuck for sixty years. Tuddenham did not look at the regional distribution of the gain. He never compared his cognitive data to the SGO’s 1920 goitre map to see if the gains were higher in the Great Lakes or the Pacific Northwest.

We do not know if he was denied access to the medical archives or if he simply chose to stay within his own academic silo.

The 2013 Merge

The reconciliation did not happen until August 2013. Three economists, Feyrer, Politi, and Weil, published a working paper that finally joined the tables.

Because the 1943 overwrite had destroyed the original AGCT scores, they had to use Air Force placement as a proxy for high cognitive ability. They merged the 1920 Defects data with the WWII draft records using modern data-linking tools.

By comparing men born just before 1924 with those born just after, the researchers caught the effect. The 15-point jump was not uniform across the country. It was concentrated exactly in the regions where goitre had been eradicated by iodised salt. The salt rollout accounted for roughly a decade of the Flynn Effect in a single stroke.

This finding broke the 1948 consensus. The economists were outside the military’s departmental structure and had no institutional reason to keep the body and mind separate. They looked across the silos that the War Department had built and maintained for nine decades.

The success had been hiding in the files all along, but the files were in different rooms.

The Shape of the Failure

This 90-year delay looks like a failure of the system itself, not a conspiracy. The SGO saw goitre as a body problem, and the AGO saw low scores as a school problem. Neither department had the conceptual framework to ask if a nutritional change in 1924 could change the test scores of 1943.

The hardware itself played a role. The 80-column limit on a punch card forced a choice between types of data.

When the clerks followed TM-12-305 and overwrote the weight field, they removed the physical evidence from the archive. The academic silo then codified the error when Tuddenham’s educational theory went unchallenged for six decades. Our investigation confirms that no proof of intent has been found. The current best explanation is neutral.

Sources

Sources include: Love and Davenport’s ‘Defects Found in Drafted Men’ (War Department, 1920); Michigan State Medical Society proceedings and Iodized Salt Committee records (1922-1924); War Department Training Manual TM-12-305 (1 May 1943); R.D. Tuddenham’s paper in ‘American Psychologist’ (1948); and Feyrer, Politi, and Weil’s NBER working paper (August 2013).