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91Ó°ÊÓ

In 2015, data collected on the monthly on-time arrival rate of major domestic and regional airlines operating between Australian airports shows a roughly bell-shaped distribution for 72 observations with \(\bar{x}=85.93\) and \(s=3\). Use the empirical rule to describe the distribution. (Source: https://bitre.gov.au/ publications/ongoing/airline_on_time_monthly.aspx).

Short Answer

Expert verified
68% falls in [82.93, 88.93], 95% in [79.93, 91.93], and 99.7% in [76.93, 94.93].

Step by step solution

01

Understand the Empirical Rule

The empirical rule states that for a normal distribution: 68% of the data falls within one standard deviation (\(s\)) of the mean (\(\bar{x}\)), 95% falls within two standard deviations, and 99.7% falls within three standard deviations.
02

Calculate One Standard Deviation Range

The range for 68% of the data is calculated by subtracting and adding one standard deviation from the mean: \( \bar{x} \pm s = 85.93 \pm 3 = [82.93, 88.93] \).
03

Calculate Two Standard Deviations Range

The range for 95% of the data is found by subtracting and adding two standard deviations: \( \bar{x} \pm 2s = 85.93 \pm 6 = [79.93, 91.93] \).
04

Calculate Three Standard Deviations Range

For 99.7% coverage, we subtract and add three standard deviations: \( \bar{x} \pm 3s = 85.93 \pm 9 = [76.93, 94.93] \). This indicates where nearly all data should fall.

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Key Concepts

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

Normal Distribution
The concept of a normal distribution is fundamental in statistics and data analysis. When data is described as having a normal distribution, it typically forms a symmetric, bell-shaped curve when graphed. This shape reflects how data tends to cluster around a central value, with frequencies fading as you move away from that center.

In a normal distribution: - The **mean** (average) is located at the center of the bell curve. - The **median** and **mode** are also situated at the peak of the curve, meaning they are equal if the distribution is perfectly normal. - Data points follow a standard deviation pattern, forming predictable ranges.

This shape makes the normal distribution a key model for observing phenomena across various fields, from natural sciences to social sciences. The characteristics of normal distribution simplify calculations and predictions, which is why it's so widely appreciated in data-driven models.
Standard Deviation
Standard deviation is a measure that quantifies the amount of variation in a set of data values. It tells us how data points spread out from the mean in a data set. In the context of a normal distribution, it helps define the shape and spread of the bell curve.

For example, in the exercise we analyzed: - The mean arrival rate was 85.93%, and the standard deviation was 3%. - These figures help illustrate that 68% of airline arrival rates fall within one standard deviation (i.e., between 82.93% and 88.93%).

This concept aids in understanding the consistency of the data: - **Low standard deviation** means data points are close to the mean, indicating uniform performance. - **High standard deviation** hints at widely spread data points, suggesting more variability or unpredictability in the dataset.

Understanding standard deviation is crucial for interpreting data distributions and making sound conclusions based on data variability.
Data Analysis
Data analysis is key in interpreting any dataset, like the airline arrival rates in our exercise. At its core, it involves extracting meaningful insights from raw data.

Key components of basic data analysis include: - **Collecting data**: Ensuring data is reliable and valid is the first step. - **Descriptive statistics**: Mean, median, mode, and standard deviation are calculated to summarize the data. - **Using the empirical rule**: In our case, it describes how data is distributed around the mean in set intervals.

Data analysis offers actionable insights: - Helps identify patterns and trends. - Supports decision-making based on empirical evidence rather than assumptions. - Allows for visualization of data to communicate findings effectively.

By thoroughly analyzing the data, stakeholders can make informed decisions, improve processes, or adjust strategies to optimize performance and outcomes based on real-world data.

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Most popular questions from this chapter

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?

In parts a and b, what shape do you expect for the distributions of electricity use and water use in a recent month in Gainesville, Florida? Why? (Data supplied by N. T. Kamhoot, Gainesville Regional Utilities.) a. Residential electricity used had mean \(=780\) and standard deviation \(=506\) kilowatt hours \((\mathrm{Kwh})\). The minimum usage was \(3 \mathrm{Kwh}\) and the maximum was \(9390 \mathrm{Kwh}\) b. Water consumption had mean \(=7100\) and standard deviation \(=6200\) (gallons).

Categorical/quantitative difference a. Explain the difference between categorical and quantitative variables. b. Give an example of each.

National Geographic Traveler magazine recently presented data on the annual number of vacation days averaged by residents of eight countries. They reported 42 days for Italy, 37 for France, 35 for Germany, 34 for Brazil, 28 for Britain, 26 for Canada, 25 for Japan, and 13 for the United States. a. Report the median. b. By finding the median of the four values below the median, report the first quartile. c. Find the third quartile. d. Interpret the values found in parts a-c in the context of these data.

a. Explain the difference between a discrete variable and a continuous variable. b. Give an example of each type.

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