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The following failure time observations (\({\bf{1000s}}\)of hours) resulted from accelerated life testing of \(16\) integrated circuit chips of a certain type:

\(\begin{array}{*{20}{l}}{82.8 11.6 359.5 502.5 307.8 179.7}\\{242.0 26.5 244.8 304.3 379.1}\\{212.6 229.9 558.9 366.7 204.6}\end{array}\)

Use the corresponding percentiles of the exponential distribution to construct a probability plot. Then explain why the plot assesses the plausibility of the sample having been generated from an exponential distribution

Short Answer

Expert verified

The created exponential probability plot contains no strong curvature, thus the distribution of the observations could be approximately exponentially distributed. And it is plausible.

Step by step solution

01

Definition of Plausibility

In contrast to probability and possibility, which provide some clues to objective reality, plausibility is simply a subject-related concept: plausibility can only exist because it is borne by human reasoning. To put it another way, something is only conceivable if someone asserts it to be so.

02

Explanation for the plausibility of the product.

Given: exponential distribution with \(\lambda = 1.\)

Given observations:

\(\begin{array}{l}82.8,11.6,359.5,502.5,307.8,179.7,242,26.5,244.8,304.3,379.1,212.6,\\229.9,558.9,366.7,204.6\end{array}\)

Sort the observations from smallest to largest:

\(\begin{array}{l}11.6,26.5,82.8,179.7,204.6,212.6,229.9,242,244.8,304.3,307.8,359.5,\\366.7,379.1,502.5,558.9\end{array}\)

We note that the data contains \(16\) data values.

We then need to determine the exponential -percentiles, which are the values of x for which the cumulative distribution function of the exponential distribution with \(\lambda = 1\)is equal to the probability

\(\frac{{i - 0.5}}{{16}}\) (or the closest probability). Note: These percentiles are the same as the Weibull percentiles (because the standard Weibull distribution is the exponential distribution with \(\lambda = 1)\)and thus the percentiles are \(\ln ( - \ln (1 - p))\)

03

Explanation for the plausibility of the product.

\(i = 1 \Rightarrow p = \frac{{1 - 0.5}}{{16}} = 0.03125 \Rightarrow z = - 3.45\)

\(\begin{array}{l}i = 2 \Rightarrow p = \frac{{2 - 0.5}}{{16}} = 0.09375 \Rightarrow z = - 2.32\\i = 3 \Rightarrow p = \frac{{3 - 0.5}}{{16}} = 0.15625 \Rightarrow z = - 1.77\\i = 4 \Rightarrow p = \frac{{4 - 0.5}}{{16}} = 0.21875 \Rightarrow z = - 1.40\\i = 5 \Rightarrow p = \frac{{5 - 0.5}}{{16}} = 0.28125 \Rightarrow z = - 1.11\end{array}\)

\(\begin{array}{l}i = 6 \Rightarrow p = \frac{{6 - 0.5}}{{16}} = 0.34375 \Rightarrow z = - 0.86\\i = 7 \Rightarrow p = \frac{{7 - 0.5}}{{16}} = 0.40625 \Rightarrow z = - 0.65\\i = 8 \Rightarrow p = \frac{{8 - 0.5}}{{16}} = 0.46875 \Rightarrow z = - 0.45\\i = 9 \Rightarrow p = \frac{{9 - 0.5}}{{16}} = 0.53125 \Rightarrow z = 0.45\\i = 10 \Rightarrow p = \frac{{10 - 0.5}}{{16}} = 0.59375 \Rightarrow z = 0.65\\i = 12 \Rightarrow p = \frac{{12 - 0.5}}{{16}} = 0.71875 \Rightarrow z = 1.11\end{array}\)

04

Explanation for the plausibility of the product.

\(\begin{array}{l}i = 13 \Rightarrow p = \frac{{13 - 0.5}}{{16}} = 0.78125 \Rightarrow z = 1.40\\i = 14 \Rightarrow p = \frac{{14 - 0.5}}{{16}} = 0.84375 \Rightarrow z = 1.77\\i = 15 \Rightarrow p = \frac{{15 - 0.5}}{{16}} = 0.90625 \Rightarrow z = 2.32\\i = 16 \Rightarrow p = \frac{{16 - 0.5}}{{16}} = 0.96875 \Rightarrow z = 3.45\end{array}\)

EXPONENTIAL PROBABILITY PLOT

To determine if the distribution of values is approximately exponentially distributed, we have to create an Exponential probability plot.

A normal probability plot is basically a scatterplot with the observations on the horizontal axis and the exponential percentiles on the vertical axis.

05

Explanation for the plausibility of the product.

If the pattern in the exponential probability plot is roughly linear and does not contain strong curvature, then it is safe to assume that the distribution of the observations is approximately exponential.

The created exponential probability plot contains no strong curvature, thus the distribution of the observations could be approximately exponentially distributed.

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Most popular questions from this chapter

The article "The Load-Life Relationship for M50 Bearings with Silicon Nitride Ceramic Balls" (Lubrication Engr., \({\rm{1984: 153 - 159}}\)) reports the accompanying data on bearing load life (million revs.) for bearings tested at a \({\rm{6}}{\rm{.45kN}}\) load.

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a. Construct a normal probability plot. Is normality plausible?

b. Construct a Weibull probability plot. Is the Weibull distribution family plausible?

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a. Compute \({\rm{E(X)}}\) and \({\rm{V(X)}}\).

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\({\rm{F(x) = }}\left\{ {\begin{array}{*{20}{c}}{\rm{0}}&{{\rm{x}} \le {\rm{0}}}\\{\frac{{\rm{x}}}{{\rm{4}}}\left( {{\rm{1 + ln}}\left( {\frac{{\rm{4}}}{{\rm{x}}}} \right)} \right)}&{{\rm{0 < x}} \le {\rm{4}}}\\{\rm{1}}&{{\rm{x > 4}}}\end{array}} \right.\)

(This type of cdf is suggested in the article 鈥淰ariability in Measured Bedload Transport Rates鈥 (Water 91影视 Bull., \({\rm{1985:39 - 48}}\)) as a model for a certain hydrologic variable.) What is a. \({\rm{P(X}} \le {\rm{1)}}\)? b. \({\rm{P(1}} \le {\rm{X}} \le {\rm{3)}}\)? c. The pdf of \({\rm{X}}\)?

Consider babies born in the 鈥渘ormal鈥 range of\(37 - 43\)weeks gestational age. Extensive data support the assumption that for such babies born in the United States, birth weight is normally distributed with a mean of\(3432 g\)and a standard deviation of\(482\)g. (The article 鈥淎re Babies Normal?鈥 analyzed data from a particular year; for a sensible choice of class intervals, a histogram did not look at all normal, but after further investigations it was determined that this was due to some hospitals measuring weight in grams and others measuring to the nearest ounce and then converting to grams. A modified choice of class intervals that allowed for this gave a histogram that was well described by a normal distribution.) a. What is the probability that the birth weight of a randomly selected baby of this type exceeds\(4000 g\)? Is between\(3000 and 4000 g\)? b. What is the probability that the birth weight of a randomly selected baby of this type is either less than\(2000 g\)or greater than\(5000 g\)? c. What is the probability that the birth weight of a randomly selected baby of this type exceeds\(7\)lb? d. How would you characterize the most extreme\(.1\% \)of all birth weights? e. If X is a random variable with a normal distribution and a is a numerical constant, then Y = X also has a normal distribution. Use this to determine the distribution of birth weight expressed in pounds (shape, mean, and standard deviation), and then recalculate the probability from part (c). How does this compare to your previous answer?

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