[2] While continuing to teach at Cherwell Hall, she became part of a group of McDougall's students, including William Brown, Cyril Burt, and J. C. Flugel, who were interested in experimental psychology.
Having been trained in experimental methods by McDougall, Smith developed and carried out a major study on the effects of fatigue.
Using herself as the sole research subject, she restricted herself to only 1.5, 3.5 and 5.5 hours of sleep on successive nights, using a variety of tests to evaluate the consequences.
These included serial word recall, the capacity to learn nonsense syllables, and performance on several physical tasks.
She also noted that the fatigued subject's ability to judge her own effectiveness was impaired, "extremely bad work being not infrequently accompanied by a conviction that it is unusually good".
This experience led to her being hired to interview incarcerated prostitutes to determine whether or not "drink had contributed largely to their choice of occupation", a hypothesis that was not supported by her findings.
[6] One of her most important contributions began with a study, in collaboration with Culpin and Eric Farmer, of a condition called "telegraphist's cramp", a type of focal dystonia of the hand which had been thought to be caused by physical fatigue.
[7] It was the basis for further research by Smith and Culpin into psychological factors in other occupational diseases, resulting in 1930 in a "landmark" report entitled The Nervous Temperament.
Demonstrating a positive correlation between Culpin's clinical assessments and Smith's test results, the study provided evidence that psychoneurosis is one of the factors responsible for industrial illness.
[6][10] From the late 1920s, her office was at the London School of Hygiene and Tropical Medicine, where she collaborated closely with the epidemiologist and statistician Major Greenwood and the medical psychologist Millais Culpin.
[1] Smith and Culpin, while part of the IFRB, studied the health of WW1 munitions workers via use of a device known as a Dotting Machine, which was made by Edgar Schuster.
After her retirement from the Industrial Health Research Board, May Smith held several positions on the executive of the British Psychological Society, of which she had been a member since 1914.