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Coverage Error

Coverage Error is due to the fact that not every unit in the population is represented on the frame. For example persons without Internet access are by definition excluded from the target population of a web survey. However, web surveys and online polls tend to advertise their results as representative of general public opinion. See box on the left for proportion of Americans that have access to the internet.This illustrates that coverage error takes into account the opinions of individuals who have graduate education and who are between the ages of 18 29. Web surveys are flawed by virtue of the fact that there is a digital divide in our nation.

Even more worrying is the practice of RDD (Random Digit Dialing) surveys which survey opinions of random individuals who own fixed phone lines. This is a common practice among surveyors to introduce a level of accuracy in terms of population that is being sampled. It is thought that RDD surveys give a more accurate picture of public opinion. However, this practice is in great danger of becoming irrelevant as RDD sampling does not take into account portion of the population that does not have telephones. This is even more pertinent today, especially with the 18 24 yr old category of the population, who tend to rely solely on cell phones and do not own fixed line telephones. Surveyors are not able to perform a random dial survey on cell phone numbers because the Federal Communications Commission also has erected do-not-call rules barring survey researchers from using RDD, to find cell-phone users. These rules also prohibit calling people who have to pay for the call.

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