In other words, "screening effect," as other researchers have already concluded. (Here's a paper by German researchers, published in January 2014 in Radiation and Environmental Biophysics.)
Even some of the Japanese experts such as Dr. Masamichi Nishio who have been fanning the fear of a big increase in thyroid cancer in children after the Fukushima I NPP accident seem to be backtracking (link goes to a togetter with Dr. Nishio's comments) these days, as the third anniversary of the triple disaster of earthquake, tsunami and nuclear accident in Japan approaches.
The Guardian's article below, however, does not make it crystal clear that the thyroid screening test being done in Fukushima Prefecture since 2011 aims to test ALL children who were 18 years old and under at the time of the nuclear accident and who would have not gone to a thyroid specialist to have their thyroids checked had there been no nuclear accident.
Fukushima Prefecture's screening is finding the cases of thyroid cancer which would have gone unnoticed and undetected for years if not decades. To compare the cancer cases found in this screening with the normal cancer cases where the patient goes to the doctor and the doctor makes diagnosis doesn't make any sense, but that's what some experts in Japan and outside Japan have been doing, to the apparent frustration (for some) and anxiety (for many others) among parents in Fukushima.
So far, 269,354 children, or about 80% of all children in Fukushima who were 18 years old and younger at the time of the accident have been tested, according to the latest report (2/7/2014; in Japanese) by the Fukushima prefectural government. None of the children found with thyroid cancer had any symptoms.
From UK's The Guardian (3/9/2014; emphasis is mine):
Fukushima's children at centre of debate over rates of thyroid cancer
Three years after the worst nuclear accident in a generation, the Japanese prefecture is reporting a rise in the number of children showing cancer symptoms. But is this directly related to the disaster, or is the testing more rigorous?
by Justin McCurry in Fukushima
When doctors found several tiny nodules on his 12-year-old daughter's thyroid gland, Toshiyuki Kamei refused to let parental fear get the better of him. The symptoms are not uncommon, and the probability that they will develop into something more serious is low.
Yet Kamei can be forgiven for occasional moments of doubt: his daughter, Ayako, is one of almost 400,000 children who were living in Fukushima on 11 March 2011 – the start of the world's worst nuclear accident for a quarter of a century.
"As a parent, of course I worry, but my daughter is taking it in her stride," said Kamei, who lives in Iwaki, a city about 40km (25 miles) south of the wrecked Fukushima Daiichi nuclear power plant. "She doesn't tell me if it's on her mind, and I've decided not to ask her about it."
Three years after the plant suffered a triple meltdown that released huge quantities of radiation into the atmosphere, medical authorities in Fukushima prefecture are reporting a significant rise in the number of thyroid cancer cases among local children and young adults.
The results have prompted a bitter debate about the potential effects the meltdown had on the health of hundreds of thousands of children. Either the higher-than-normal rates of thyroid cancer are connected to the nuclear accident, or they are the inevitable result of a testing regime unprecedented in size, and conducted using state-of-the-art medical equipment.
Last month, the number of confirmed and suspected cases of thyroid cancer among people aged 18 or below at the time of the accident rose to 75, compared with 59 at the end of last September. Of the current total, 33 cases have been confirmed as cancer.
...At first sight, the figures give cause for alarm. Thyroid cancer normally affects one to two people per million among 10 to 14-year-olds in Japan, a rate far lower than observed in Fukushima, although tests there apply to people aged up to 18.
But experts familiar with both disasters caution against making similarly gloomy predictions for the children of Fukushima. Dillwyn Williams, emeritus professor of pathology at Cambridge University, pointed out that a noticeable increase in thyroid cancers was not observed until three to four years after the Chernobyl accident.
"Much less radioactivity was released from Fukushima than from Chernobyl," he said. "Most of [the Fukushima radiation] was blown over the Pacific Ocean, and thyroid doses in the most-affected areas are low compared to Chernobyl.
"It is very unlikely there will be a large increase in thyroid cancer or any other health problems, apart from anxiety and psychological difficulties. That does not mean the surveillance should stop. There were surprises after Chernobyl and there may be again after Fukushima."
Williams and other experts have attributed the large number of cases to the use of hypersensitive ultrasound, which can detect the tiniest lesions, and the large number of children being tested.
...Gerry Thomas, professor of molecular pathology at Imperial College, London University, blames growing anxiety among Fukushima residents on "pseudo-scientists who can shout louder than real scientists".
"The biggest effect will be psychological – just as it was post-Chernobyl," said Thomas, who insists the rising number of cases is due to comprehensive screening, not radiation. "I still stick with what I have always said: there will not be a single death due to the radiological consequences of this accident."
(Full article at the link)
Ah. The curse of "one in million" continues, but at least the article mentions "comprehensive screening".
Professor Geraldine Thomas sounds somewhat like Mr. George Monbiot, or lot like Professor Wade Allison of Oxford University, but her comment that "pseudo-scientists" causing anxiety among Fukushima residents has a point, I believe, after reading numerous articles from the Japanese newspapers on the 3rd anniversary of the nuclear accident.