Researchers produced a study that involved 875 workers in the auto industry. The study showed that after 30 years 367 were retired, 85 were still employed in the auto industry, 300 left the industry, and the rest were not reachable. What is the problem with this study?

Question

anonymous · Answer

A>voluntary response 
b> self interest 
 c>precise numbers 
d> missing data

anonymous · Answer

i'm not sure this has any relation to mathematics , could you explain the problem more ?