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One of the questions asked in a Pew Research Center/USA Today poll taken in June, 2013 , was: "Overall, do you approve or disapprove of the government's collection of telephone and internet data as part of anti-terrorism efforts?" (http://www,pollingreport.com/terrorhtm). of the 1512 respondents, 48% said "approve," 47% said "disapprove," and the rest were unsure. a. What is the conservative margin of error for this poll? b. Use the conservative margin of error to find a \(95 \%\) confidence interval for the proportion of all adults who would have answered "approve" if asked. c. Repeat part (b) for the answer "disapprove." d. Compare the confidence intervals in parts (b) and (c). From those intervals, can you conclude that one of the two opinions (approve or disapprove) was held by a majority of the population at that time? Explain.

Short Answer

Expert verified
Calculate margin of error as 2.57%. Using this, neither "approve" nor "disapprove" holds a clear majority.

Step by step solution

01

Calculate Sample Size

The poll surveyed 1512 respondents. This is our sample size ( and it will be used to calculate the standard error.
02

Find Conservative Margin of Error Formula

The conservative margin of error formula is \[\text{Margin of Error (ME)} = \frac{1}{\sqrt{n}} \]where \(n\) is the sample size.
03

Calculate Margin of Error

Substitute 1512 for \(n\) to find the margin of error:\[ \text{ME} = \frac{1}{\sqrt{1512}} \approx 0.0257 \text{ or } 2.57\% \]This is the conservative margin of error.
04

Calculate Confidence Interval for "Approve"

The percentage that approved is 48%. Use the margin of error to find the confidence interval:\[ \text{Lower limit} = 0.48 - 0.0257 = 0.4543 \]\[ \text{Upper limit} = 0.48 + 0.0257 = 0.5057 \]The 95% confidence interval for "approve" is approximately 45.43% to 50.57%.
05

Calculate Confidence Interval for "Disapprove"

The percentage that disapproved is 47%. Use the margin of error to find the confidence interval:\[ \text{Lower limit} = 0.47 - 0.0257 = 0.4443 \]\[ \text{Upper limit} = 0.47 + 0.0257 = 0.4957 \]The 95% confidence interval for "disapprove" is approximately 44.43% to 49.57%.
06

Compare Confidence Intervals

The confidence intervals for "approve" and "disapprove" overlap (45.43% to 50.57% for approval and 44.43% to 49.57% for disapproval). Because of this overlap and the margin of error, neither opinion holds a clear majority; we cannot conclusively say one opinion was more prevalent than the other based on this poll.

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Margin of Error
The Margin of Error is a critical component of survey analysis and polling data as it helps to understand the accuracy of the survey results. In simpler terms, the margin of error reflects the degree to which the survey results might deviate from the true population values. Think of it as a buffer that accounts for any variations between the sample surveyed and the overall population.

A useful formula to remember is \( \text{Margin of Error (ME)} = \frac{1}{\sqrt{n}} \), where \( n \) is the sample size. This formula provides a "conservative" estimate, meaning it's usually larger than necessary to ensure we're not underestimating the potential error.

In our example, the margin of error was calculated as approximately 2.57%, providing an understanding of how much the survey results can be trusted. This means if the survey indicates that 48% approve, the actual approval rate might be 2.57% higher or lower.
Survey Analysis
Survey analysis is the process of interpreting the data collected from a survey to draw conclusions about the broader population. It involves taking raw data and conducting various calculations and assessments to understand what it represents.

One of the primary goals of survey analysis is to construct confidence intervals. These intervals provide a range within which the true population parameter, such as the proportion that approves or disapproves of a policy, likely falls. By understanding and applying margin of error in the context of survey analysis, we can estimate the actual support or opposition levels among a larger group beyond those surveyed.
  • Helps to draw conclusions about broader trends.
  • Includes breakdown of calculated metrics like the margin of error, percentage approvals, and more.
  • Relies heavily on statistical tools to interpret survey data accurately.
Analyzing survey data is crucial, as it guides policymakers, businesses and researchers in making informed decisions.
Polling Data
Polling data is widely used to gauge public opinion on a variety of topics, from political issues to consumer preferences. Understanding and analyzing polling data is essential to make predictions and adjustments in strategies.

In the provided exercise, the polling data showed 48% approval and 47% disapproval out of 1512 respondents. Polls like these are snapshots of how the public feels about an issue at a given time. But, since all polls have some level of error due to the sampling process, understanding the accompanying margin of error is vital to interpret these results accurately.

It's also important to consider that, often, a portion of respondents may be undecided or provide no opinion, which can further affect the clarity of the results. These aspects must be factored in to avoid misrepresenting what the polling data indicates.
Statistical Inference
Statistical inference is about making predictions or decisions about a population based on sampled data. It involves examining a small, manageable segment of a larger population to draw conclusions about the whole.

In the context of the exercise, statistical inference was used to estimate the broader public opinion on government data collection. By analyzing a subset of the population (the 1512 respondents), and incorporating statistical tools like margin of error and confidence intervals, one can infer how the entire population might respond.
  • Allows us to extrapolate the survey results to a general population level.
  • Underpins many types of data analysis, including election forecasts and marketing research.
  • Relies on tools like confidence intervals to convey the reliability of predictions.
This makes statistical inference a powerful tool in science and social studies, providing a foundational understanding to support decision-making across various fields.

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Most popular questions from this chapter

On September \(10,1998,\) the "Starr Report," alleging impeachable offenses by President Bill Clinton, was released to Congress. That evening, the Gallup Organization conducted a poll of 645 adults nationwide to assess initial reaction (reported at www.gallup.com). One of the questions asked was: "Based on what you know at this point, do you think that Bill Clinton should or should not be impeached and removed from office?" The response "Yes, should" was selected by 31\% of the respondents. a. The Gallup webpage said, "For results based on the total sample of adults nationwide, one can say with \(95 \%\) confidence that the margin of sampling error is no greater than ±4 percentage points." Explain what this means and verify that the statement is accurate. b. Give a \(95 \%\) confidence interval for the percentage of all adults who would have said President Clinton should be impeached had they been asked that evening. c.A similar Gallup Poll taken a few months earlier, in June 1998 , found that \(19 \%\) responded that President Clinton should be impeached. Do you think the difference between the results of the two polls can be attributed to chance variation in the samples taken, or does it represent a real difference of opinion in the population in June versus mid-September? Explain.

Parade Magazine reported that "nearly 3200 readers dialed a 900 number to respond to a survey in our Jan. 8 cover story on America's young people and violence" (19 February 1995, p. 20). Of those responding, "63.3\% say they have been victims or personally know a victim of violent crime." Can the results quoted and methods in this chapter legitimately be used to compute a \(95 \%\) confidence interval for the proportion of Americans who fit that description? If so, compute the interval. If not, explain why not. (Note that calling a 900 number was not a free call at the time; the caller was charged a fee.)

What level of confidence would accompany each of the following intervals? a. Sample proportion $$\pm 1.0(S E P)$$ b. Sample proportion \(\pm 1.645(S E P)\) c. Sample proportion \(\pm 1.96(S E P)\) d. Sample proportion \(\pm 2.576(S E P)\)

An advertisement for Seldane-D, a (now discontinued) drug prescribed for seasonal allergic rhinitis, reported results of a double-blind study in which 374 patients took Seldane-D and 193 took a placebo (Time, 27 March 1995, p. 18). Headaches were reported as a side effect by 65 of those taking Seldane-D. a. What is the sample proportion of Seldane-D takers who reported headaches? b. What is the standard error accompanying the proportion computed in part (a)? c. Construct a \(95 \%\) confidence interval for the population proportion based on the information from parts (a) and (b). d. Interpret the confidence interval from part (c) by writing a few sentences explaining what it means.

A telephone poll reported in Time magazine ( 6 February \(1995,\) p. 24 ) asked 359 adult Americans the question: "Do you think Congress should maintain or repeal last year's ban on several types of assault weapons?" Seventy-five percent responded "maintain." a. Compute the standard error that accompanies the sample proportion of .75 b. Time reported that the "sampling error is \(\pm 4.5 \% . "\) Verify that \(4.5 \%\) is approximately what would be added and subtracted to the sample percentage to create a \(95 \%\) confidence interval. (Note that it is equivalent to a margin of error of .045 for a confidence interval for the population proportion.) c. Use the information reported by Time to create a \(95 \%\) confidence interval for the population proportion. Interpret the interval in words that would be understood by someone with no training in statistics. Be sure to specify the population to which it applies. d. The ban was in place for 10 years, but repealed in 2004 . In 2013 , after some high-profile cases of gun violence, the topic was in the news again. In March, 2013 , a Quinnipiac University poll asked 1711 adults: "Do you support or oppose a nationwide ban on the sale of assault weapons?" Fifty-nine percent said "Support." (Source: http://www.pollingreport.com/guns.htm). Find a 95\% confidence interval for the population proportion that supported this ban in March, 2013. e. Compare the confidence intervals found in parts (c) and (d). Write a few sentences explaining whether support for banning these weapons seemed to increase or decrease between 1994 and 2013.

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