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Evaluating public opinion data: lesson summary

Public opinion polls can only tell us so much about the outcome of elections and public policy.

Common problems with polls

ProblemWhy it's misleading
improper sampling techniquesSamples should be random, otherwise poll results might not accurately represent the target population.
biased questionsIt’s tough for questions to be truly unbiased, but questions framed to portray candidates or policies in a positive or negative light can strongly influence responses.
small sample sizeThe smaller the sample size, the larger the margin of error. A survey of ten people is unlikely to turn up results consistent with the preferences of the entire population of the United States. Mass surveys usually have a sample size of at least 1000 individuals.
large or unreported sampling errorThe results from a sample won’t exactly represent a population. This is called sampling error, and the likely size of the error is called the margin of error. Researchers should report their poll’s margin of error. If a poll reports that 58% of Americans prefer a candidate, but the margin of error is 10%, researchers should not conclude that the majority of Americans prefer the candidate (since the true percentage could be as little as 48%).
lack of transparency in methodsReliable polls publish the methods by which researchers collected the data. Without this information, it’s impossible to judge whether the researchers followed scientific procedures.

How much does public opinion data really tell us?

The media breathlessly reports the results of polls. During a presidential election, news outlets broadcast the result of opinion polls on a daily basis, showing one candidate ahead on Monday and the other candidate ahead on Tuesday. Did the public’s opinion really shift that much in just 24 hours?
Even more perplexing are notable differences between public opinion and the actions of government officials. Generally, politicians hoping for reelection want to please their constituents, so it seems logical that they would align their policies with the results of public opinion polls. But there are plenty of examples of mismatches between public opinion and public policy. For example, polls consistently reveal that the majority of Americans support stricter gun control measures, but few elected officials have proposed legislation restricting firearms. What accounts for this difference between opinion and action?
Public opinion polls can only tell us so much about the outcome of elections and public policy. In some cases, this is because the data itself was not reliable, or was presented in a misleading fashion. In other cases, the disconnect results from situations where public opinion was not the driving factor behind a political opinion.

Review questions: know your graphs

News outlets, campaigns, and corporations frequently publish graphs to illustrate the results of public opinion polls. But graphs can be misleading, even if the information they contain is technically correct!
1. Here's an unscientific graph. Can you identify two problems with it?
2. Here's a misleading graph. Can you identify two ways it's misleading?

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