To have a reasonable certainty in the conclusions, many thousands of cases are required to detect the increased risk of lung cancer due to radon. This is because the more things that cause a disease the harder it is to separate one cause from another, thus it takes many cases to pinpoint the risk from each separate cause. The U.S. Public Health Service radon experts estimate that 10,000 to 30,000 cases, and twice as many controls would be needed to conduct a definitive epidemiologic study of residential radon lung cancer risk. The residential studies conducted to date have all included between 50 and 1500 cases and thus have been too small to provide conclusive information.
Some years ago this same process was used to detect an increased risk of lung cancer due to cigarette smoking. It took many years of study to make the positive link between the cause and effect of smoking and lung cancer. Most of the increased lung cancer risk is attributable to smoking through mathematical modeling. The research process for smoking was very laborious. However, radon's process is even more challenging because radon's contribution to increased lung cancer risk (12%) is difficult to see against the large background of lung cancer due to other causes, which include smoking, asbestos, some heavy metals and other types of radiation; i.e., detecting radon-related lung cancer is like trying to detect a 12% increase of sand on a beach already full of sand.
Finally, it is difficult to accurately determine radon exposures in residential settings since we are estimating past exposures from current measurements. The number of required study participants increases with the difficulty in determining the exposure.
Why are residential epidemiology studies of radon so complicated?
There are many factors that must be considered when designing a residential radon epidemiology study. It is very expensive and often impossible to design a study that takes all the pertinent factors into consideration. These factors include:
- Mobility: people move a lot over their lifetime; it is virtually impossible to go back and test every home where an individual has lived;
- >Housing Stock Changes: over time, older homes are often destroyed or remodeled, thus radon measurements will be non-existent or highly varied; a home's radon level may change, higher or lower, over time if new ventilation systems are installed, the occupancy patterns are substantially different, or the home's foundation shifts or cracks appear.
- Inaccurate Histories: often a majority of the lung cancer cases (individuals) being studied are deceased or too sick to be interviewed by researchers. This requires reliance on second-hand information which may not be as accurate. These inaccuracies primarily affect:
- Residence History: a child or other relative may not be aware of all residences occupied by the patient - particularly if the occupancy is distant in time or of relatively short duration. Even if the surrogate respondent is aware of a residence they may not have enough additional information to allow researchers to locate the home.
- Smoking History: smoking history historically has reliability problems. Individuals may under-estimate the amount they smoke. Conversely, relatives or friends may over-estimate smoking history.
- Other: complicating factors other than variations in smoking habits include an individual's: genetics, lifestyle, exposure to other carcinogens, and home heating, venting and air conditioning preferences.