In order to be accurate questions had to be asked without bias in the correct context. Understanding public opinion around the 1930s required relying on one's instincts, which were not always correct. Today public opinion is the concern of more then just journalists and politicians. Market researchers, television networks, political consulting firms and interest groups are all active in polling and surveys. Surveys and polls have become an everyday occurrence and are no longer concentrated during pre-election periods.
Independent agencies have databases full of information available to the public.
Professionalism has grown and efficiency has increased. It is easier to contact people and keep records of responses. Training is now available as well. Although methods of polling have improved, it is still not foolproof. Who is asked as well as how it is asked can affect a person's response.