It's clear from the passage that polling companies _____.

Opinion polls have been developed largely since the 1930s as a scientific way of learning what large numbers of people think about various topics. They are used extensively in the fields of politics and marketing. Many polling companies provide political candidates and manufacturers with information that shows how they are viewed by members of the public. This information is often used in developing advertising programs and planning the strategy of political campaigns. The results of these private polls, either in politics or in marketing are usually confidential and not available to the public.