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Consider the following 10 observations on the lifetime (in hours) for a certain type of component: $$ \begin{array}{lllll} 152.7 & 172.0 & 172.5 & 173.3 & 193.0 \\ 204.7 & 216.5 & 234.9 & 262.6 & 422.6 \end{array} $$ Construct a normal probability plot, and comment on the plausibility of a normal distribution as a model for component lifetime.

Short Answer

Expert verified
After calculating the corresponding z-score for each observation, plot the graph of observed values against the z-scores. The resulting plot will evidently verify the normality or non-normality of the given data. An approximate straight line suggests a normal distribution.

Step by step solution

01

Arranging and Normalizing the data

First, arrange the data in ascending order. Then, calculate the quantiles for each observation by using the formula \( q = \frac{i - 0.5}{N} \) where \( i \) is the position of the term in the ordered dataset and \( N \) is the total number of observations. This will yield a set of expected probabilities under a normal distribution.
02

Calculating Probabilities

Next, calculate the corresponding z-scores from the standard normal distribution for each of the calculated probabilities from step one. The z-score is the signed number of standard deviations an individual data point is from the mean. This can be done using a standard normal distribution table or calculator function. The result is the theoretical value of the component lifetime if it were distributed normally.
03

Plotting the data

Plot a graph where the x-axis represents the observed component lifetimes and the y-axis represents the corresponding z-scores calculated in step two.
04

Interpreting the results

Interpret the results based on the plot. If the points lie approximately on a straight line, then the data is normal. Otherwise, if they deviate from a straight line, the data is not normally distributed.

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Key Concepts

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

Component Lifetime Analysis
Component lifetime analysis involves examining how long a particular component is expected to function before failing. This type of analysis is crucial for determining the reliability of products and predicting maintenance or replacement schedules. By understanding the typical lifespan of a component, industries can plan for repairs or replacements, thus avoiding costly downtimes.

For the type of component given in the original exercise, this analysis begins with collecting data about how long each component lasts during usage. Once this data is collected, it's essential to assess whether it follows a common statistical distribution, such as normal distribution. If the data fits well into this distribution, it becomes easier to predict future component performance using statistical models. These predictions help engineers and managers in planning preventive measures and making informed decisions about component designs.
Normal Distribution
The normal distribution is a foundational concept in statistics and is often referred to as the Gaussian distribution. It is characterized by its bell-shaped curve, with most of the data points clustering around the mean. The normal distribution is used to model a wide range of natural phenomena, making it a valuable tool for statistical analysis.

In component lifetime analysis, evaluating whether the lifetime data of components follows a normal distribution can help predict failure rates and optimize maintenance schedules. A normally distributed dataset implies that most components will have lifetimes close to the mean, with fewer components significantly underperforming or overperforming.
  • The mean, median, and mode of a normal distribution are all equal.
  • It is symmetric about the mean.
  • The total area under the curve is 1.
When data appears to follow a normal distribution, using statistical tools designed for normally distributed data becomes more effective, enabling better projections and decision-making.
Z-scores
Z-scores are a statistical measurement that describes a data point's relation to the mean of a group of data. A z-score tells us how many standard deviations a data point is from the mean. This is crucial for understanding data in the context of a standard normal distribution.

A positive z-score indicates the data point is above the mean, while a negative z-score indicates it is below the mean. Z-scores are used extensively in probability calculations and to test hypotheses. In the context of the exercise, calculating z-scores allows us to compare the ordered lifetime data of components to standard normal distribution values. This comparison facilitates the construction of a normal probability plot, which is pivotal for assessing the normality of the dataset.
Data Normalization
Data normalization is the process of rescaling data so that it falls within a certain range, typically 0 to 1. This is a vital preprocessing step that ensures fair comparison across different datasets. In statistical analyses involving z-scores and normal distribution, normalization simplifies the interpretation and comparison of data.

Normalizing data involves adjusting the values measured on different scales to a common scale. In the context of the given exercise, normalization helps in computing corresponding quantiles that express probabilities of a distribution. These standard scores, once calculated, are crucial to understanding how far from the mean each individual data point lies.

This step is often followed by plotting the normalized data against theoretical distribution values or in constructing probability plots. By visualizing the normalized data against a theoretical model, deviations can be easily spotted, making it clear whether the dataset follows the expected distribution pattern.

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Most popular questions from this chapter

Classify each of the following numerical variables as either discrete or continuous: a. The fuel efficiency (in miles per gallon) of an automobile b. The amount of rainfall at a particular location during the next year c. The distance that a person throws a baseball d. The number of questions asked during a 1-hour lecture e. The tension (in pounds per square inch) at which a tennis racket is strung f. The amount of water used by a household during a given month g. The number of traffic citations issued by the highway patrol in a particular county on a given day

Ecologists have long been interested in factors that might explain how far north or south particular animal species are found. As part of one such study, the paper "Temperature and the Northern Distributions of Wintering Birds鈥 (Ecology [1991]: 2274-2285) gave the following body masses (in grams) for 50 different bird species that had previously been thought to have northern boundaries corresponding to a particular isotherm: $$ \begin{array}{rrrrrrrr} 7.7 & 10.1 & 21.6 & 8.6 & 12.0 & 11.4 & 16.6 & 9.4 \\ 11.5 & 9.0 & 8.2 & 20.2 & 48.5 & 21.6 & 26.1 & 6.2 \\ 19.1 & 21.0 & 28.1 & 10.6 & 31.6 & 6.7 & 5.0 & 68.8 \\ 23.9 & 19.8 & 20.1 & 6.0 & 99.6 & 19.8 & 16.5 & 9.0 \\ 448.0 & 21.3 & 17.4 & 36.9 & 34.0 & 41.0 & 15.9 & 12.5 \\ 10.2 & 31.0 & 21.5 & 11.9 & 32.5 & 9.8 & 93.9 & 10.9 \\ 19.6 & 14.5 & & & & & & \end{array} $$ a. Construct a stem-and-leaf display in which 448.0 is shown beside the display as an outlier value, the stem of an observation is the tens digit, the leaf is the ones digit, and the tenths digit is suppressed (for example, 21.5 has stem 2 and leaf 1 ). What do you perceive as the most prominent feature of the display? b. Draw a histogram based on the class intervals 5 to \(<10,10\) to \(<15,15\) to \(<20,20\) to \(<25,25\) to \(<30\) 30 to \(<40,40\) to \(<50,50\) to \(<100,\) and 100 to \(<500\). Is a transformation of the data desirable? Explain. c. Use a calculator or statistical computer package to calculate logarithms of these observations and construct a histogram. Is the logarithmic transformation satisfactory? d. Consider transformed value \(=\frac{1}{\sqrt{\text { original value }}}\) and construct a histogram of the transformed data. Does it appear to resemble a normal distribution?

The size of the left upper chamber of the heart is one measure of cardiovascular health. When the upper left chamber is enlarged, the risk of heart problems is increased. The paper "Left Atrial Size Increases with Body Mass Index in Children" (International Journal of Cardiology [2009]: \(1-7\) ) described a study in which the left atrial size was measured for a large number of children age 5 to 15 years. Based on these data, the authors concluded that for healthy children, left atrial diameter was approximately normally distributed with a mean of 26.4 millimeters and a standard deviation of 4.2 millimeters. a. Approximately what proportion of healthy children has left atrial diameters less than 24 millimeters? b. Approximately what proportion of healthy children has left atrial diameters greater than 32 millimeters? c. Approximately what proportion of healthy children has left atrial diameters between 25 and 30 millimeters? d. For healthy children, what is the value for which only about \(20 \%\) have a larger left atrial diameter?

Determine the value \(z^{*}\) that a. Separates the largest \(3 \%\) of all \(z\) values from the others b. Separates the largest \(1 \%\) of all \(z\) values from the others c. Separates the smallest \(4 \%\) of all \(z\) values from the others d. Separates the smallest \(10 \%\) of all \(z\) values from the others

State whether each of the following numerical variables is discrete or continuous: a. The number of defective tires on a car b. The body temperature of a hospital patient c. The number of pages in a book d. The number of checkout lines operating at a large grocery store e. The lifetime of a lightbulb

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