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91Ó°ÊÓ

Consider the following statement: More than \(65 \%\) of the residents of Los Angeles earn less than the average wage for that city. Could this statement be correct? If so, how? If not, why not?

Short Answer

Expert verified
Yes, the statement could be correct. The wage distribution in a city is often right-skewed, which means a small number of residents earn much more than the rest. This pulls up the average wage making it possible that more than 65% of the residents earn less than the average wage for the city.

Step by step solution

01

Understanding Average and Median

The first concept we need to understand is the difference between an average and a median. An average, also known as the mean, is calculated by adding all of the values together, then dividing by the number of values. The median is the middle value, which separates the higher half from the lower half of data set. If we order the income of all residents in ascending order, the income that would be in the middle will be the median.
02

Understanding the Wage Distribution

In an evenly distributed set of values, the average and the median would be almost the same. However, in a skewed distribution, especially if it is skewed towards higher values (right-skewed), the mean will be greater than the median. This occurs because the high wage earners pull up the average wage.
03

Analyzing the Statement

In the context of this problem, the statement would mean that the wage distribution is skewed towards higher values (right-skewed). This is because fewer people earn a lot more which can pull up the 'average' wage. Therefore more than 65% of people can actually earn less than the average wage since the average is not a good representation of central tendency in a skewed distribution.

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Key Concepts

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

Mean vs Median
When exploring the concepts of mean and median, it's crucial to recognize their distinct characteristics. Both metrics serve to summarize data, yet they capture different aspects. The mean is what we typically understand as the "average." It is computed by summing all the values in a dataset and dividing by the number of entries. This statistic gives us a single number that represents an "average" value across all observations.

The median, on the other hand, finds the middle value of an ordered dataset. This involves arranging the data in sequential order and identifying the central number. If you have an even count of numbers, the median will be the average of the two middle numbers. Unlike the mean, the median isn't influenced by extremely high or low values, making it a more robust measure in certain scenarios.

In situations where a dataset displays extreme values or outliers, the mean could provide a misleading picture. However, the median guards against such discrepancies by focusing solely on the central value, offering a measure less affected by extremes.
Skewed Distribution
A skewed distribution occurs when the values in a dataset are not symmetrically distributed. Instead, they tend to cluster more to one side, creating a tail on one end of the data. This skewness can be left or right, depending on where the longer tail is.

  • Right Skewed: When the tail on the right side is longer, we refer to it as a right-skewed or positively skewed distribution. In such instances, there are a few extremely high values, dragging the mean upwards.
  • Left Skewed: Conversely, when the tail extends more to the left, it is a left-skewed distribution, indicating the presence of low values that pull the mean downwards.

In the context of salary distributions like in Los Angeles, one might encounter a right skew. This means while there are some individuals with very high earnings, the majority earn considerably less. As a result, a significant portion of the population earns below the mean because the mean is disproportionately affected by these rare but high salaries.
Central Tendency
Central tendency refers to the metric that identifies the "center" of a dataset. This can be revelatory in understanding the general behavior of data distributions. There are several measures of central tendency, but the common types include mean, median, and mode

The selection of the most suitable central tendency measure often depends on the data's nature and the context of analysis. For instance, in a normal distribution where data is symmetrically spread, mean and median would yield similar values. In such cases, the mean can effectively summarize the dataset as a whole.

However, in skewed distributions, as frequently seen in income or wealth distribution, the median becomes more trustworthy. It is less affected by outliers and skewed data, providing a more accurate indicator of what a typical observation might be. Understanding which measure to rely on requires careful analysis of how data is distributed, ensuring that conclusions drawn are both meaningful and accurate.

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Most popular questions from this chapter

The average playing time of compact discs in a large collection is 35 minutes, and the standard deviation is 5 minutes. a. What value is 1 standard deviation above the mean? 1 standard deviation below the mean? What values are 2 standard deviations away from the mean? b. Without assuming anything about the distribution of times, at least what percentage of the times is between 25 and 45 minutes? c. Without assuming anything about the distribution of times, what can be said about the percentage of times that are either less than 20 minutes or greater than 50 minutes? d. Assuming that the distribution of times is approximately normal, about what percentage of times are between 25 and 45 minutes? less than 20 minutes or greater than 50 minutes? less than 20 minutes?

In a study investigating the effect of car speed on accident severity, 5000 reports of fatal automobile accidents were examined, and the vehicle speed at impact was recorded for each one. For these 5000 accidents, the average speed was \(42 \mathrm{mph}\) and the standard deviation was \(15 \mathrm{mph}\). A histogram revealed that the vehicle speed at impact distribution was approximately normal. a. Roughly what proportion of vehicle speeds were between 27 and \(57 \mathrm{mph}\) ? b. Roughly what proportion of vehicle speeds exceeded \(57 \mathrm{mph}\) ?

The accompanying data on number of minutes used for cell phone calls in one month was generated to be consistent with summary statistics published in a report of a marketing study of San Diego residents (TeleTruth, March 2009 ): $$ \begin{array}{rrrrrrrrrr} 189 & 0 & 189 & 177 & 106 & 201 & 0 & 212 & 0 & 306 \\ 0 & 0 & 59 & 224 & 0 & 189 & 142 & 83 & 71 & 165 \\ 236 & 0 & 142 & 236 & 130 & & & & & \end{array} $$ a. Would you recommend the mean or the median as a measure of center for this data set? Give a brief explanation of your choice. (Hint: It may help to look at a graphical display of the data.) b. Compute a trimmed mean by deleting the three smallest observations and the three largest observations in the data set and then averaging the remaining 19 observations. What is the trimming percentage for this trimmed mean? c. What trimming percentage would you need to use in order to delete all of the 0 minute values from the data set? Would you recommend a trimmed mean with this trimming percentage? Explain why or why not.

Give two sets of five numbers that have the same mean but different standard deviations, and give two sets of five numbers that have the same standard deviation but different means.

The average reading speed of students completing a speed-reading course is 450 words per minute (wpm). If the standard deviation is \(70 \mathrm{wpm}\), find the \(z\) score associated with each of the following reading speeds. a. \(320 \mathrm{wpm}\) c. \(420 \mathrm{wpm}\) b. \(475 \mathrm{wpm}\) d. \(610 \mathrm{wpm}\)

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