<p>Press Prime on Polling (Part 1)</p><p>By Terry Clark, Journalism Professor University of Central Oklahoma</p><p>Polling can be very accurate, as with Nate Silver's "538" that called every state in 2012. Some can be very misleading. How to know?</p><p>Hence, here's the prof's press primer on polling, part one. </p><p>Definition of terms is first. - Population - The group to be surveyed, such as likely voters, residents of Hennessey, Thunder season ticket holders. - Random - Random does not mean "haphazard." It means that every person in the population has an equal chance of being chosen. It's easy in a classroom - you put every name in a hat and have a few names pulled out. Bigger groups require phone numbers or addresses, all more easily available than ever with computer data. - Sample - The portion of the population to be chosen randomly to ask the poll questions. - Valid - A poll is valid if the results collected from the sample can be applied to the entire population. - Margin of error Ð Expressed as a plus and minus percentage. Every poll has flaws and variables that will affect the accuracy of the results, but the larger the sample, the lower the margin of error. (If you poll everyone in the population there will be no margin of error, but that isn't possible in most cases). </p><p>Now the key question - how big a sample do you need to conduct an accurate poll? </p><p>You're not going to believe the answer. Timing, wording of questions, training of the pollsters, polling methods, and other factors also affect a poll's validity, not just the sample size. And sample size is not dependent on "population" size. </p><p>That said, to get a sense of how people in Oklahoma might vote on "Right to Farm" or another issue, you need roughly only 400 registered, or likely, voters selected randomly for a five percent margin of error. Yep, that's all. </p><p>Here's how the margin of error figures. Suppose a poll of 400 Panhandle voters shows they favor seceding from the state by a 52-48 percent margin. The results are within the margin of error so the election could go either way - it could be 52-43, or 47-52, or any combination. If, on the other hand, the vote was 75-25 percent, Oklahoma, you have a problem. </p><p>Most national polls try to have a sample of about 1,200 people - for a margin of error of about plus and minus three percent. </p><p>Also important in polling is the timing. As fast as things change in this digital news country, today's polls might not be accurate in two days. Other factors can affect outcome. But that's a separate subject - next month, an American's checklist for evaluating a poll. </p>