[ RadSafe ] Can anyone help with this mystery?

[Bernard Cohen]

 A paper by W.N. Sont et al in Am. J. Epidemiol. 154:309-318:2001 on 
radiation monitored Canadian workers in industrial, medical, dental, and 
nuclear power jobs gives the following percentages of people dying from 
cancer vs lifetime accumulated radiation dose (as I crudely calculate 
from the data they present):

          Dose        % who died      95% confid.             

          in rem      from cancer      interval     

            0.25             1.8%             1.8 - 1.8       

             0.75            2.3%             1.9 - 2.7      

             1.5              2.8%             2.4 - 3.2        

             3.5              2.5%             2.1 - 2.9        

              7.5             3.9%             3.2 - 4.6        

              15              3.8%             2.9 - 4.7        

              30              4.8%             3.3 - 6.3        

            >40              6.8%             3.4 - 4.2        

          On the face of it, these data give very strong evidence in 
favor of a linear-no threshold dose response relationship extending well 
below 1.0 rem.

          However, by the time a person dies, he receives a dose 
averaging about 20 rem from non-occupational exposure, and these 
exposures vary widely, typically between about 10 rem and 30 rem, in a 
manner not correlated with occupational exposures. Roughly speaking, 
that means that the numbers for dose in the first column above should be 
increased by about 20 rem and assigned an uncertaincy of about 10 rem.

          Crudely, this converts the above table to:

         

          Dose        % who died      95% confid.             

          in rem      from cancer      interval     

 

     10.25-30.25      1.8%             1.8 - 1.8     
                                                                   
10.75     -30.75      2.3%             1.9 - 2.7      

      11.5-31.5         2.8%             2.4 - 3.2        

      13.5-33.5         2.5%             2.1 - 2.9        

      17.5-37.5         3.9%             3.2 - 4.6        

         25-45             3.8%             2.9 - 4.7        

          40-60            4.8%             3.3 - 6.3        

            >50              6.8%             3.4 - 4.2            

 

          No one could claim that this table gives any info on low level 
radiation in the dose range below 20 rem. But this raises another 
question: why was the first table so deceiving?

            Can anyone offer an explanation for this?