Future cancers from Fukushima plant may be hidden/ AP

As long as the research is methodologically sound and designed to capture a broad range of possible adverse outcomes from radiation released at Fukushima (where people have been exposed to many different isotopes through skin contact, inhalation and ingestion at widely varying doses), you will probably learn a lot about how the radiation affected health.  However, if you limit what you are looking for to only a few outcomes, such as childhood thyroid cancer, you will never identify the full range or number of adverse effects.  From today's article by the AP's Malcolm Ritter:

Even if the worst nuclear accident in 25 years leads to many people developing cancer, we may never find out.Looking back on those early days of radiation horror, that may sound implausible....

The idea that Fukushima-related cancers may go undetected gives no comfort to Edwin Lyman, a physicist and senior scientist with the Union of Concerned Scientists, a group that advocates for nuclear safety. He said that even if cancers don't turn up in population studies, that "doesn't mean the cancers aren't there, and it doesn't mean it doesn't matter."

"I think that a prediction of thousands of cancer deaths as a result of the radiation from Fukushima is not out of line," Lyman said. But he stressed that authorities can do a lot to limit the toll by reducing future exposure to the radiation. That could mean expensive decontamination projects, large areas of condemned land and people never returning home, he said. "There's some difficult choices ahead."

Japan's Cabinet this month endorsed a plan to cut contamination levels in half within the next two years. The government recently announced it plans to study the risk from long-term exposure to the low-dose radiation level used as a trigger for evacuations...

Eisuke Matsui, a lung cancer specialist and a former associate professor at Gifu University School of Medicine, criticized the project.  He said it appears to largely ignore potential radiation-induced health risks like diabetes, cataracts and heart problems that have been hinted at by some studies of Chernobyl.
"If thyroid cancer is virtually the only abnormality on which they are focusing, I must say there is a big question mark over the reliability of this survey," he said.
He also suggested sampling hair, clipped nails and fallen baby teeth to test for radioactive isotopes such as strontium that are undetectable by the survey's current approach.
"We should check as many potential problems as possible," Matsui said.
Yasumura acknowledges the main purpose of his study is "to relieve radiation fears." But Matsui says he has a problem with that.
"A health survey should be a start," Matsui says, "not a goal."  [In other words, if you already have the outcome in mind, your study is biased before it starts.--Nass]
Tatsuhiko Kodama, head of the Radioisotope Center at the University of Tokyo, urged quick action to determine the cancer risks.
He said big population surveys and analysis will take so long that it would make more sense to run a careful simulation of radiation exposures and do anything possible to reduce the risks.
"Our responsibility is to tell the people now what possible risks may be to their health," he said.