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According to a recent report from the U.S. National Center for Health Statistics, females between 25 and 34 years of age have a bell-shaped distribution for height, with mean of 65 inches and standard deviation of 3.5 inches. a. Give an interval within which about \(95 \%\) of the heights fall. b. What is the height for a female who is 3 standard deviations below the mean? Would this be a rather unusual height? Why?

Short Answer

Expert verified
About 95% of heights fall between 58 and 72 inches. A height of 54.5 inches is unusual as it's 3 standard deviations below the mean.

Step by step solution

01

Understanding the 95% Interval

In a normal distribution, approximately 95% of the data falls within two standard deviations of the mean. Therefore, to find this interval, we take the mean, which is 65 inches, and calculate the mean minus and plus two times the standard deviation.
02

Calculate the Lower Bound

To calculate the lower bound of the 95% interval, subtract two standard deviations from the mean: \[ 65 - 2 \times 3.5 = 65 - 7 = 58 \] Thus, the lower bound is 58 inches.
03

Calculate the Upper Bound

To find the upper bound, add two standard deviations to the mean:\[ 65 + 2 \times 3.5 = 65 + 7 = 72 \] Thus, the upper bound is 72 inches.
04

Interval Solution

The interval within which about 95% of the heights will fall is between 58 inches and 72 inches.
05

Understand 3 Standard Deviations Below Mean

To find the height for a female who is 3 standard deviations below the mean, subtract three times the standard deviation from the mean. This gives us:\[ 65 - 3 \times 3.5 = 65 - 10.5 = 54.5 \] Thus, the height is 54.5 inches.
06

Determine the Unusualness of the Height

A height that is three standard deviations below the mean is considered quite unusual in a normal distribution since about 99.7% of data falls within three standard deviations. A result beyond this range (like 54.5 inches) is rare.

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Key Concepts

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

Standard Deviation
Standard deviation is a fundamental concept in statistics. It tells us how spread out the numbers in a data set are. When you see a smaller standard deviation, it means that the data points are close to the mean. However, a larger standard deviation indicates that the data is more spread out.

In terms of the problem at hand, the standard deviation given is 3.5 inches. This helps us understand the variation in height of females between the ages 25 to 34. The larger this value, the more varied the heights would be. It's important as it helps us determine how common or unusual a particular height is compared to the average height. Always remember, in a normal distribution, about 68% of the data falls within one standard deviation of the mean, 95% within two, and 99.7% within three. This is crucial to determining intervals like the 95% confidence interval.
Mean
The mean, often referred to as the average, is one of the most common measures of central tendency. It is calculated by summing up all the numbers in a data set and then dividing by the number of data points. The mean gives us a central value to understand where the middle of a data set lies.

For this exercise, the mean height is given as 65 inches. This means that, on average, females between 25 to 34 years old are about 65 inches tall. It serves as a reference point for other calculations, like standard deviation and confidence intervals. When you know the mean, you can better understand the nature of the data and how other values compare to this central point.
95% Confidence Interval
A 95% confidence interval in a normal distribution gives us an area where we expect 95% of the data values to fall. To calculate this interval, we take two times the standard deviation and subtract and add these from the mean.

In this exercise, the mean height is 65 inches, and the standard deviation is 3.5 inches. Therefore, we subtract and add twice this value (7 inches) from the mean. The interval becomes 58 inches to 72 inches. This means that we can be confident that about 95% of the females' heights fall within this range.

This concept is crucial in statistics because it provides a way to estimate the range where most values lie, giving insights into the data's uncertainty and reliability.
Statistics Education
Statistics education involves learning how to collect, analyze, and interpret data effectively. Essential concepts include understanding measures like the mean, median, standard deviation, and confidence intervals.

Through such education, one gains the ability to interpret statistical data in various fields like health, economics, and social sciences. For example, understanding a normal distribution is critical for evaluating whether a data point, like a height of 54.5 inches, is unusual. Since this height falls three standard deviations below the mean, it's considered rare.

Being adept at statistics empowers individuals to make informed decisions based on data, appreciate data representation, and critically analyze statistical arguments. It fosters analytical thinking and helps in interpreting the significance and implications of various statistical results in real-world scenarios.

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Most popular questions from this chapter

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