Opinion poll is an inquiry into public opinion conducted by interviewing on random sample of people before actual Election Day and it includes all people who may or may not vote. On the contrary, Exit poll is taken of a sample of voters leaving the polling booth who have actually cast their votes. Their verdict is definite and indicates the final results and can be used to predict the outcome of an election. While exit poll has no bearing on election results, the opinion poll do influence the election and as a result, some political parties are not in favor of opinion poll.
If not adulterated opinion polls are useful in many ways. Now a day's people are educated and they know very well the importance of a good political system. Every party tries to woo people by their campaigns and promise to fulfill their dream if voted to power. People look at these campaigns carefully and select candidates whom they think has capability to fulfill their aspirations.
However, there are some people who are unable to decide right candidates and they are influenced by opinion poll. Opinion poll is a reaction taken from people who are very sure about their choice of candidate. So opinion poll helps those people who are undecided about their choice of candidates. In this sense opinion polls are not only useful but also helpful in increasing voting percentage.
Recently Congress party had reported to the Election Commission to ban opinion polls but the BJP was not in favor of such ban. Congress had earlier supported opinion poll but this time it was in favor of ban. The simple reason id opinion poll did not predict its win. Whereas the BJP supported opinion poll because it predicted the results in its favor.
However, many a times it has been found that the predictions and the actual results were completely different. For example, in the 2004 General Elections, opinion polls predicted that the National Democratic Alliance (NDA) would again come to power. However, in reality, the Congress formed the government. Even in the 2007 Uttar Pradesh state elections, not a single opinion poll predicted that the Bahujan Samaj Party (BSP) would form a government. But Mayawati came to power proving all predictions wrong. We cannot ignore the fact that to predict election results of such a massive and diverse country on basis of some samples is very difficult, but nonetheless it's a scientific principle to know the trend and the mood of the voters.
The criticism about the opinion poll is always about the framing of the questions and the methodology used to collect the opinion. In fact, the exact wordings of questions and the series of question have its importance. Similarly, the method of getting the answers, whether it was through a phone call (selected or random), e-mail, web based-survey or personal visit, is also important. The sample group, its demographic behavior, its economic status and various other factors also make a great difference in tabulating the opinion. It is also possible that parties can bribe opinion pollsters to show them as a winning party and can influence voters.
In spite of such criticism, opinion polls are necessary as they are useful in deciding the most favored party before the elections, provided if they are conducted with full honesty. Also it helps undecided voters to decide the right candidate.
However, opinion poll is not the sole criteria for the choosing the political party or candidates. In fact many people do not care about opinion poll results at all. They select their candidate using their own wisdom and sometime also keep opinion poll results in mind.
So banning of opinion poll is not a good idea in a democratic country like ours. Even having restrictions on it is undesirable.