Prof Richard Wakeford, from the University of Manchester's Centre for Occupational and Environmental Health, points out that health studies look for a "signal" of a specific health effect linked to Chernobyl.
They aim to pick out that signal above the "background noise" from other causes. That has been incredibly difficult, primarily because of the huge background noise that was the almost simultaneous upheaval of the Soviet Union's collapse.
"It's assumed that there will be some cancers linked to the accident in addition to the thyroid cancers, but detecting them amid that socioeconomic chaos - that had its own impacts on people's health - has proven almost impossible," says Prof Wakeford. Cancer also affects between a third and a half of people in Europe, so any Chernobyl signal is likely to be small.