/*! This file is auto-generated */ .wp-block-button__link{color:#fff;background-color:#32373c;border-radius:9999px;box-shadow:none;text-decoration:none;padding:calc(.667em + 2px) calc(1.333em + 2px);font-size:1.125em}.wp-block-file__button{background:#32373c;color:#fff;text-decoration:none} Problem 9 Over the past 50 years, there ha... [FREE SOLUTION] | 91Ó°ÊÓ

91Ó°ÊÓ

Over the past 50 years, there has been a strong negative correlation between average annual income and the record time to run I mile. In other words, average annual incomes have been rising while the record time to run 1 mile has been decreasing. (a) Do you think increasing incomes cause decreasing times to run the mile? Explain. (b) What lurking variables might be causing the change in one or both of the variables? Explain.

Short Answer

Expert verified
(a) No, increasing incomes likely do not cause faster mile times. (b) Lurking variables include advancements in technology, training, nutrition, and medical support.

Step by step solution

01

Understanding Correlation vs. Causation

A strong negative correlation means that as one variable increases, the other decreases. However, correlation does not imply causation. Just because two variables show a strong correlation, it does not mean one causes the other.
02

Analysis of Part (a)

Consider the question of whether increasing incomes cause decreased mile times. While there is a correlation, rising incomes do not necessarily cause faster mile times. Many factors can contribute to improved athletic performance, such as better training methods and increased access to sports science.
03

Identification of Lurking Variables for Part (b)

Lurking variables might influence both average income and mile times. For instance, technological advancements could lead to better training equipment and sports techniques, indirectly causing more productive economies and faster athletic performances. Improved nutrition and medical support could also benefit both socioeconomic conditions and physical fitness outcomes.

Unlock Step-by-Step Solutions & Ace Your Exams!

  • Full Textbook Solutions

    Get detailed explanations and key concepts

  • Unlimited Al creation

    Al flashcards, explanations, exams and more...

  • Ads-free access

    To over 500 millions flashcards

  • Money-back guarantee

    We refund you if you fail your exam.

Over 30 million students worldwide already upgrade their learning with 91Ó°ÊÓ!

Key Concepts

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

Negative Correlation
Understanding a "negative correlation" is key to analyzing data patterns over time. When two variables show a negative correlation, it means that as one variable increases, the other tends to decrease. In our example, we see a trend between average annual income and the record time to run a mile. As incomes rise, mile record times fall. Remember, correlation does not mean one variable causes changes in another. This concept is often pivotal in statistical analysis where recognizing "correlation vs. causation" helps us ask the right questions. Questions like: "Why do these trends exist?" or "What external factors might be influencing these patterns?" Understanding negative correlation aids in untangling complex data for more effective decision-making.
Lurking Variables
Lurking variables are hidden factors that affect the variables being studied, even if they aren't immediately obvious. They can complicate analysis, as they may provide alternative explanations for observed correlations. In our scenario, lurking variables might explain why there is a negative correlation between income and mile run performance. These variables can include:
  • Advancements in sports technology: improved equipment and apparel can boost athletic performances.
  • Better training techniques: as we learn more about the science of athletics, training methods evolve.
  • Nutrition and healthcare advancements: as societies grow richer, access to better nutrition and healthcare improves, influencing both general health and athletic success.
Considering lurking variables helps create a complete picture in statistical studies, guiding more nuanced conclusions.
Athletic Performance
Athletic performance is influenced by numerous factors that can change over time. These include access to better training facilities, improved knowledge of sports science, and even societal changes like income increases. As communities prosper, there are more resources available for athletes to hone their skills.
  • Training Methods: Advances in understanding physiology and biomechanics have led to more effective training regimes.
  • Equipment: Modern equipment can reduce injury risks and enhance performance.
  • Nutrition: A balanced diet fuels better performance; improved access to quality food aids athletic success.
  • Health Care: Access to top-notch medical care supports injury prevention and recovery.
These factors must be considered when evaluating trends in sports performances over time.
Statistical Analysis
Statistical analysis is the process through which data is collected, examined, and interpreted to uncover patterns or trends. In the study of correlations, such as between income and running times, statistical methods can help clarify relationships. Here are some steps in performing statistical analysis effectively:
  • Data Collection: Ensure data is reliable and representative of the population.
  • Identifying Variables: Clearly define which variables are being analyzed, and consider potential lurking variables.
  • Using Statistical Tools: Employ tools like regressions or correlation coefficients to explore relationships.
  • Interpretation: Look beyond numbers to understand what your data is telling you, considering external factors.
  • Conclusions: Use findings to ask new questions or guide further research for actionable insights.
The process of statistical analysis helps uncover deeper insights into how different factors might relate, ultimately guiding smarter decision-making.

One App. One Place for Learning.

All the tools & learning materials you need for study success - in one app.

Get started for free

Most popular questions from this chapter

(a) Suppose \(n=6\) and the sample correlation coefficient is \(r=0.90 .\) Is \(r\) significant at the \(1 \%\) level of significance (based on a two-tailed test)? (b) Suppose \(n=10\) and the sample correlation coefficient is \(r=0.90 .\) Is \(r\) significant at the \(1 \%\) level of significance (based on a two-tailed test)? (c) Explain why the test results of parts (a) and (b) are different even though the sample correlation coefficient \(r=0.90\) is the same in both parts. Does it appear that sample size plays an important role in determining the significance of a correlation coefficient? Explain.

When we use a least-squares line to predict \(y\) values for \(x\) values beyond the range of \(x\) values found in the data, are we extrapolating or interpolating? Are there any concerns about such predictions?

If two variables have a negative linear correlation, is the slope of the least-squares line positive or negative?

Wolf packs tend to be large extended family groups that have a well-defined hunting territory. Wolves not in the pack are driven out of the territory or killed. In ecologically similar regions, is the size of an extended wolf pack related to size of hunting region? Using radio collars on wolves, the size of the hunting region can be estimated for a given pack of wolves. Let \(x\) represent the number of wolves in an extended pack and \(y\) represent the size of the hunting region in \(\mathrm{km}^{2} / 1000 .\) From Denali National Park we have the following data. $$\begin{array}{l|ccccc}\hline x \text { wolves } & 26 & 37 & 22 & 69 & 98 \\\\\hline y \mathrm{km}^{2} / 1000 & 7.38 & 12.13 & 8.18 & 15.36 & 16.81 \\\\\hline\end{array}$$ Reference: The Wolves of Denali by Mech, Adams, Meier, Burch, and Dale, University of Minnesota Press. (a) Verify that \(\Sigma x=252, \Sigma y=59.86, \Sigma x^{2}=16,894, \Sigma y^{2}=787.0194\) \(\Sigma x y=3527.87,\) and \(r \approx 0.9405\) (b) Use a \(1 \%\) level of significance to test the claim \(\rho>0\) (c) Verify that \(S_{e} \approx 1.6453, a \approx 5.8309,\) and \(b \approx 0.12185\) (d) Find the predicted size of the hunting region for an extended pack of 42 wolves. (e) Find an \(85 \%\) confidence interval for your prediction of part (d). (f) Use a \(1 \%\) level of significance to test the claim that \(\beta>0\) (g) Find a \(95 \%\) confidence interval for \(\beta\) and interpret its meaning in terms of territory size per wolf.

Please do the following. (a) Draw a scatter diagram displaying the data. (b) Verify the given sums \(\Sigma x, \Sigma y, \Sigma x^{2}, \Sigma y^{2},\) and \(\Sigma x y\) and the value of the sample correlation coefficient \(r\) (c) Find \(\bar{x}, \bar{y}, a,\) and \(b .\) Then find the equation of the least- squares line \(\hat{y}=a+b x\) (d) Graph the least-squares line on your scatter diagram. Be sure to use the point \((\bar{x}, \bar{y})\) as one of the points on the line. (e) Interpretation Find the value of the coefficient of determination \(r^{2} .\) What percentage of the variation in \(y\) can be explained by the corresponding variation in \(x\) and the least-squares line? What percentage is unexplained? Answers may vary slightly due to rounding. Jobs An economist is studying the job market in Denver-area neighborhoods. Let \(x\) represent the total number of jobs in a given neighborhood, and let \(y\) represent the number of entry-level jobs in the same neighborhood. A sample of six Denver neighborhoods gave the following information (units in hundreds of jobs).Complete parts (a) through (e), given \(2 x=202,2 y=28, \Sigma x^{2}=7754\) \(\Sigma y^{2}=164, \Sigma x y=1096,\) and \(r \approx 0.860\) (f) For a neighborhood with \(x=40\) jobs, how many are predicted to be entry- level jobs?

See all solutions

Recommended explanations on Math Textbooks

View all explanations

What do you think about this solution?

We value your feedback to improve our textbook solutions.

Study anywhere. Anytime. Across all devices.