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a. If a rifleman's gunsight is adjusted incorrectly, he might shoot bullets consistently close to 2 feet left of the bull's-eye target. Draw a sketch of the target with the bullet holes. Does this show lack of precision or bias? b. Draw a second sketch of the target if the shots are both unbiased and precise (have little variation). The rifleman's aim is not perfect, so your sketches should show more than one bullet hole.

Short Answer

Expert verified
In the first scenario, the consistent leftward placement of the bullet holes indicates bias. In the second scenario, the shots are both unbiased and precise as shown by the bullet holes clustering around the bull's-eye.

Step by step solution

01

Sketching the First Scenario

Draw a target and mark the bull's-eye at its center. Then, place several bullet hole marks approximately 2 feet to the left of the bull's-eye. Ensure the bullet holes are close to each other. This distribution of bullet holes represents consistent shooting to the left side.
02

Analysis of the First Scenario

Considering the bullet holes which are clustered together but not near the bull's-eye, this demonstrates a bias in the shooting. The shots repeatedly fall to the same side of the target, meaning the shooting is biased rather than lacking precision.
03

Sketching the Second Scenario

Now draw a new target. In this case, make several bullet hole marks close to the bull's-eye and in a close cluster. They must spread around the bull's-eye slightly due to imperfect aim but still close to each other and to the bull's-eye.
04

Analysis of the Second Scenario

This scenario illustrates that the shooting is both unbiased and precise. The bullet holes are not concentrated to one side but rather are spread around the bull's-eye, showing no bias. The proximity of the bullet holes to each other signifies the precision in the rifleman's shots.

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Key Concepts

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

Bias in Statistics
Understanding bias in statistics is pivotal for anyone involved in data analysis or research. Bias refers to any systematic error that results in a consistent deviation from the true measure or value. Consider a rifleman with a misaligned gunsight: despite his skill, all his bullets hit 2 feet to the left of the target's bull's-eye. This deviation is akin to bias in statistical terms — it's not random but a consistent error affecting the entire dataset.

For data to provide legitimate insights, we need to recognize and correct bias. This might involve recalibrating equipment, as you would a gunsight, or adjusting statistical models to account for known biases. Only with unbiased data can researchers draw accurate conclusions and make reliable predictions.
Precision in Measurements
Precision in measurements speaks to the consistency and repeatability of data points. Imagine our rifleman now aiming with a well-adjusted sight. If the shots group tightly around the bull's-eye, it indicates high precision. Each attempt closely replicates the previous one, minimizing random variation, which is the hallmark of precision.

In the context of statistical analysis, precision allows us to be confident that repeating an experiment or survey under the same conditions will yield closely similar outcomes. It is important to note that precision does not necessarily imply that the measurements are correct or unbiased — you can have a precise but biased set of data.
Statistical Analysis
Statistical analysis is the science of collecting, exploring, and presenting large quantities of data to discover underlying patterns and trends. It involves various techniques to perform such explorations, summarizing vast datasets with measures of central tendencies like the mean or median, and inferring the spread of data with measures of dispersion like standard deviation or variance.

Through statistical analysis, data can reveal trends, correlations, or predictions that are not readily apparent. It's like studying a target range after a shooting practice session. You assess where most bullets hit to ascertain accuracy (central tendency) and how spread out the bullet holes are to evaluate precision (dispersion).
Data Distribution
Data distribution represents how observations are spread across a range of values. It's a foundational concept in statistics because it influences the types of statistical tests used and the conclusions drawn from data. There are various kinds of distributions, such as normal, skewed, or uniform, each providing different insights into the nature of the data.

A target with bullet holes dispersed evenly suggests a uniform distribution, while one with most holes clustering at the center and fewer as you move away indicates a normal distribution. Understanding the distribution helps in choosing the right tools for analysis and for making robust inferences from statistical data.

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Most popular questions from this chapter

A random sample of likely voters showed that \(55 \%\) planned to vote for Candidate \(\mathrm{X}\), with a margin of error of 2 percentage points and with a \(95 \%\) confidence level. a. Use a carefully worded sentence to report the \(95 \%\) confidence interval for the percentage of voters who plan to vote for Candidate \(\mathrm{X}\). b. Is there evidence that Candidate \(\mathrm{X}\) could lose. c. Suppose the survey was taken on the streets of New York City and the candidate was running for U.S. president. Explain how that would affect your conclusion.

A random sample of likely voters showed that \(49 \%\) planned to support Measure \(\mathrm{X}\). The margin of error is 3 percentage points with a \(95 \%\) confidence level. a. Using a carefully worded sentence, report the \(95 \%\) confidence interval for the percentage of voters who plan to support Measure \(X\). b. Is there evidence that Measure X will fail? c. Suppose the survey was taken on the streets of Miami and the measure was a Florida statewide measure. Explain how that would affect your conclusion.

In 2017 , the journal Obesity reported on trends in sugar-sweetened beverage (SSB) consumption. A random sample of youths aged 12 to 19 years old were asked to monitor all food and beverages consumed in a 24 -hour period. The study was done in 2003 and repeated in 2014 . The numbers who consumed a sugary beverage such as soda or fruit juice in a day are shown in the table. (Bleich et al., "Trends in Beverage Consumption among Children and Adults, 2003-2014," Obesity, vol. 26 [2018]: 432-441. doi:10.1002/oby.22056) $$ \begin{array}{|l|l|} \hline \text { Consumed SSB } & \mathbf{2 0 0 3} & \mathbf{2 0 1 4} \\ \hline \text { Yes } & 3416 & 2682 \\ \hline \text { No } & 685 & 1419 \\ \hline \end{array} $$ a. Calculate and compare the percentages of youths in this age group who consumed an SSB during the recording period. b. Check that the conditions for using a two-population confidence interval hold. c. Find the \(95 \%\) confidence interval for the difference in the proportion of youth consuming an SSB in 2003 and 2014. Based on your confidence interval, do you think there has been a change in sugar-sweetened beverage consumption among this age group? Explain.

Assume your class has 30 students and you want a random sample of 10 of them. A student suggests asking each student to flip a coin, and if the coin comes up heads, then he or she is in your sample. Explain why this is not a good method.

Explain the difference between sampling with replacement and sampling without replacement. Suppose you have the names of 10 students, each written on a 3 -inch by 5 -inch notecard, and want to select two names. Describe both procedures.

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