Guest on the occasion of the release of his new book Your future on prescription (published by Laffont) Saturday on the show What an era! on France 2, doctor Frédéric Saldmann stated: “in three weeks of vacation we lose 20 points of intelligence quotient”.
Promoting sequential fasting, the cardiologist and nutritionist is launched by Léa Salamé: “ […] on the intellectual side there are lots of little tips, it’s not just fasting, there’s also never sleeping in, and not taking too many vacations! You say we become stupid after three weeks of vacation, and I must say that you are right. »
The passage in question provoked numerous negative or mocking reactions on social networks. THE replay of the show is available on the France Télévision website (the passage in question is around 1h29).
Looking for the lost item
Contacted by 20 minutes regarding the sources on which he relies to assert that vacations cause a loss of IQ points, Frédéric Saldmann explains: “I based myself on a German study, carried out on a group of 120 people between 20 and 60 years old, who had took a test before and after the vacation. » The doctor specifies in particular that “the loss was greater in people over 40 years old. »
Frédéric Saldmann indicates the name of the journal, the study in question and those of these authors: “”The effect of vacation length on cognitive performance: A longitudinal study” Schwarzer, G., Schulz, R., & Gerst, M. (2009). Journal of Applied Psychology, 94 (2), 375-383.” Problem: no trace of this study on the Internet. Issue 94 of Journal of Applied Psychologypublished in 2009, does exist, but does not contain any article of that name. Pages 371 to 391 are occupied by another article. A search using the name of the researchers does not allow you to put your finger on the famous study either.
A study cited many times, never sourced
Subsequently, Frédéric Saldmann will cite another researcher, more easily identifiable: the German psychologist Siegfriend Lehrl (died in 2023). In fact, there are numerous press articles on the Internet attributing a study showing that three weeks of vacation could cause a loss of 20 IQ points.
However, again, we have not been able to get our hands on the research article, mentions of which can be found at least from the year 2000 in press titles. In a recent article, Release identifies the article in question (mentioned by Siegfriend Lehrl in another publication): a study called “Die Talfahrt des IQ im Krankenhaus” (“The decline in IQ in the hospital”), published in 1984.
Unfortunately, this study itself cannot be found online. When contacted, the University of Erlangen-Nuremberg, where Siegfriend Lehrl spent the majority of his academic career, was unable to provide further information.
A drop in IQ that “seems very implausible”
For researcher Franck Ramus, specialized in cognitive sciences and research director at the CNRS, a drop of 20 IQ points following a three-week vacation “seems very implausible”: “we know that general intelligence measured by IQ scores are stable throughout life. There is a margin of error: from one test to another it can fluctuate by a few points, in particular because of the conditions of administration. But a variation of 20 points I’ve never seen that, it would require a brain injury. »
A drop in academic level (different from IQ, therefore) due to the holidays is nevertheless possible, and scientifically documented. “Among students during the summer holidays, their performance in tests drops a little, they forget some of the subjects. This is a well-established effect, representing one tenth of a standard deviation, which could be compared to 1.5 IQ points. If indeed this decline in education reflects a decline in intelligence,” specifies Franck Ramus.
A meta analysis published in 1996 concluded, for example, that “knowledge test scores decline during summer vacation” and that “the effect of summer vacation was more detrimental for mathematics than for reading and more detrimental for numeracy and spelling mathematics”. Although these differences in academic performance are well established, they are by no means definitive. They also vary, particularly depending on the socio-cultural background of the student, and the activities they may have benefited from during their vacation.