4-2 Probability Plots

# 4-2 Probability Plots - Lecture 4-2 Probability Plots...

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Lecture 4-2 Probability Plots Navidi Section 4.5 1

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Does your sample come from a Normal Distribution? If large number of samples, plot Histogram Probability plots (discussed next) If small number, difficult to determine Samples from Normal distributions rarely contain outliers; if you have an outlier you would not generally use the Normal distribution If no outliers, information about process can be used 2
3 Probability Plots Scientists and engineers often work with data that can be thought of as a random sample from some population. In many cases, it is important to determine the probability distribution that approximately describes the population. More often than not, the only way to determine an appropriate distribution is to examine the sample to find a sample distribution that fits.

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Probability Plots If we had, say, 5 data points that came from a Normal distribution, what would they look like? ) ( z z
Constructing a Normal Probability Plot 5 Example: Do these five data points come from a Normal Distribution? 3.01, 3.35, 4.79, 5.96, 7.89 Assign increasing, evenly spaced values between 0 and 1 to each Xi, to denote its position in the ordered sample. To do this, use the Empirical Cumulative Distribution Function (ECDF): ECDF:

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• Summer '16
• Normal Distribution, Cumulative distribution function, Normal probability plot, probability plots

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