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In each of the following scenarios, determine if the data are paired. (a) We would like to know if Intel's stock and Southwest Airlines' stock have similar rates of return. To find out, we take a random sample of 50 days, and record Intel's and Southwest's stock on those same days. (b) We randomly sample 50 items from Target stores and note the price for each. Then we visit Walmart and collect the price for each of those same 50 items. (c) A school board would like to determine whether there is a difference in average SAT scores for students at one high school versus another high school in the district. To check, they take a simple random sample of 100 students from each high school.

Short Answer

Expert verified
(a) Paired (b) Paired (c) Not paired

Step by step solution

01

Understanding Paired Data

Paired data occurs when there is a natural pairing between two sets of observations. This pairing usually means that each observation in one set is related or corresponds to an observation in the other set.
02

Analyze Scenario (a)

In scenario (a), we have collected data on Intel's stock and Southwest Airlines' stock on the same 50 days. This indicates a pairing, as each day's observation for Intel corresponds to an observation for Southwest on that same day. Thus, the data are paired in this case.
03

Analyze Scenario (b)

In scenario (b), we take prices for 50 items from Target and then look for those same items in Walmart. Here, each item’s price in Target has a corresponding price in Walmart, forming a natural pairing between the two sets. Therefore, this scenario involves paired data.
04

Analyze Scenario (c)

In scenario (c), 100 students are randomly selected from each of two different high schools. There's no indication that each student from one school corresponds to a student in the other school. Thus, the observations from each school are independent, and the data are not paired.

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Key Concepts

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

Stock Market Analysis
In stock market analysis, understanding paired data is crucial when comparing the performance of different stocks. When two stocks' rates of return are measured on the same days, as in the case of Intel's and Southwest Airlines' stocks, each observation for one stock corresponds directly to an observation for the other stock on the same day. This creates a clearly defined set of paired data.

By using paired data in stock analysis, researchers can gain insights into how the stocks might be influenced by similar market forces on those specific days.
  • This method helps in identifying correlation and causation, which might not be as clear when using unpaired data.
  • It enhances the accuracy of comparative analyses since both stocks are subject to the same external factors on each observed day.


Such pairing allows analysts to remove a range of variables, focusing solely on the performance differences or similarities between the stocks themselves. This makes it an insightful tool for investors and financial analysts interested in drawing comparisons within the stock market.
Price Comparison
Price comparison often requires the use of paired data to ensure accuracy and reliability of the results. In our scenario with Target and Walmart, each item's price from Target is matched with its corresponding price at Walmart. This paired approach is beneficial for several reasons.

  • It ensures that a direct line of comparison is established for each individual product, leading to more meaningful insights.
  • By directly comparing prices on a per-item basis, discrepancies stand out clearly, helping in identifying which retailer offers better value for specific items.


Using paired data in price comparison is often more effective than looking at average prices across stores, which may obscure specific differences. It also allows consumers and retailers to pinpoint pricing strategies and conduct competitive analysis efficiently.

This method of comparison is widely used by businesses for market strategy adjustment and by consumers looking for the best deals.
SAT Scores
When analyzing SAT scores from students, whether they are from the same school or different schools, the concept of paired data helps address specific research questions about educational performance. However, as illustrated in our scenario of comparing high school SAT scores, paired data is not applicable.

Since the students from two different high schools are independently sampled, it means there isn't a direct pairing between students from the two schools. This is important to note because pairing can affect the methods used for statistical analysis.

When data are not paired, using comparison methods like independent sample t-tests become more appropriate as opposed to paired t-tests, which require a clear pairing of individual observations.

  • This setup can provide insights into the overall difference in scores across schools but lacks specific pair-by-pair comparison due to the absence of a natural pair relationship.
  • It reflects on the variability of educational environments without confounding the data with unnecessary pairings.


Understanding whether to use paired data or not can significantly impact the results and conclusions derived from such analyses, making it a key consideration in studies involving academic performance and comparisons.

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Most popular questions from this chapter

Air quality measurements were collected in a random sample of 25 country capitals in 2013, and then again in the same cities in 2014. We would like to use these data to compare average air quality between the two years. Should we use a paired or non-paired test? Explain your reasoning.

The standard deviation of SAT scores for students at a particular Ivy League college is 250 points. Two statistics students, Raina and Luke, want to estimate the average SAT score of students at this college as part of a class project. They want their margin of error to be no more than 25 points. (a) Raina wants to use a \(90 \%\) confidence interval. How large a sample should she collect? (b) Luke wants to use a \(99 \%\) confidence interval. Without calculating the actual sample size, determine whether his sample should be larger or smaller than Raina's, and explain your reasoning. (c) Calculate the minimum required sample size for Luke.

A \(90 \%\) confidence interval for a population mean is \((65,77) .\) The population distribution is approximately normal and the population standard deviation is unknown. This confidence interval is based on a simple random sample of 25 observations. Calculate the sample mean, the margin of error, and the sample standard deviation.

The distribution of the number of eggs laid by a certain species of hen during their breeding period has a mean of 35 eggs with a standard deviation of \(18.2 .\) Suppose a group of researchers randomly samples 45 hens of this species, counts the number of eggs laid during their breeding period, and records the sample mean. They repeat this 1,000 times, and build a distribution of sample means. (a) What is this distribution called? (b) Would you expect the shape of this distribution to be symmetric, right skewed, or left skewed? Explain your reasoning. (c) Calculate the variability of this distribution and state the appropriate term used to refer to this value. (d) Suppose the researchers' budget is reduced and they are only able to collect random samples of 10 hens. The sample mean of the number of eggs is recorded, and we repeat this 1,000 times, and build a new distribution of sample means. How will the variability of this new distribution compare to the variability of the original distribution?

In Exercise 7.24, we discussed diamond prices (standardized by weight) for diamonds with weights 0. 99 carats and 1 carat. See the table for summary statistics, and then construct a \(95 \%\) confidence interval for the average difference between the standardized prices of 0.99 and 1 carat diamonds. You may assume the conditions for inference are met. $$\begin{array}{lcc} \hline & 0.99 \text { carats } & \text { 1 carat } \\ \hline \text { Mean } & \$ 44.51 & \$ 56.81 \\ \text { SD } & \$ 13.32 & \$ 16.13 \\ \text { n } & 23 & 23 \\ \hline \end{array}$$

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