d.In order to be confident that the sample represents the population without bias, we must have a random sample. Read the following excerpt from the Pew Research methodology for this College Days “A majority of Pew Research Center surveys are conducted among the U.S. general public by telephone using a sampling method known as random digit dialing or “RDD.” This method ensures that all telephone numbers in the U.S – whether landline or cellphone – have a known chance of being included. As a result, samples based on RDD should be unbiased, and a margin of sampling error and a confidence level can be computed for them.Is this a random sample? How do you know? Introduction:Our goal in statistical inference is to infer something about a population from asample. For example, suppose that researchers want to estimate the proportion ofthe population of U.S. adults that support the death penalty. It is too expensiveand difficult to survey every U.S. adult. So researchers will poll a random sampleof U.S. adults and use the sample proportion to draw a conclusion about thepopulation proportion.In this activity we will learn about one type of statistical inference called aconfidence interval. We construct a confidence interval when our goal is toestimatea population proportion.College Days, Reconsidered% who say doing each of the following while they wereundergraduates would have better prepared them to getthe job they wantedGaining morework experience50Studying harder38Looking forwork sooner30Choosing adifferent major29Note: Based on those with atleasta bachelor's degree (n=790).Voluntary responses of "Maybe" notincluded.PEW RESEARCH CENTERQ228-dExample: Constructing a confidence intervalfrom a poll.The Pew Research Center asked collegegraduates what they could have done, whilestill in school, to be better prepared for theirdream job.We will use the results of this poll to estimatethe proportion of the population of all collegegraduates who wished they had studiedharder.In the report, the researchers state that thepoll had a margin of error of 4.3 percentagepoints at the 95% confidence level.Source: http://www.pewresearch.org/methodology/u-s-survey-research/sampling/

Random sample is essential to hypothesis testing.

A majority of Pew Research Center surveys are conducted among the U.S. general public by telephone using a sampling method known as random digit dialing or “RDD.” This method ensures that all telephone numbers in the U.S – whether landline or cellphone – have a known chance of being included. As a result, samples based on RDD should be unbiased, and a margin of sampling error and a confidence level can be computed for them. Is this a random sample? How do you know?