Unformatted text preview: Quiz 1 Scope This is a closed book and notes quiz related to Chapter 1 and associated R scripts. The scope is given below. Hopefully many will get a perfect scope. 1. Be able to use words to describe density plots as in Figure 1.11 2. Be able to write the definitions of the mean and median on page 25 and page 27. Memorize them. 3. Be able to cross of enough numbers in a sorted sample to produce a 20 percent trimmed mean by taking the mean of the remaining numbers. 4. Be able write the R syntax to produce a vector called x from a set of numbers such as 3, 5, 7,8 and to compute the mean, the median, the variance and the standard deviation of the numbers. x = c(3, 5, 7, 8) mean(x) median(x) var(x) sd(x) 5. Be able to write the R syntax to produce a histogram, a density plot and box plot for data in a vector called y. hist(y) densityplot(y) boxplot(y)µ 6. Be able to assess the skewness or symmetry from density plots using the mean and median as in Figure 1.15 7. If x1, x2, and x3 are the 3 values of a population write the three deviations from the population mean. Deviations from the population mean μ μ μ To compute the population variance we square the deviations and average these squared values. 8. If x1, x2, and x3 are the values of a sample, write the three deviations from the sample mean. Deviations from the sample mean If we square these deviations and average the results we have to multiple by an additional factor larger than 1 to obtain the sample variance. For a sample of size n, what is this factor? 9. The text describes the construction of box plots in terms of fourths. Many box plots use the 1st quartile in place of the lower fourth and the 3rd quartile in place of the upper fourth and the interquartile range instead of the fourth spread. Memorize the definition of outliers below that uses the language of quartiles and interquartile range. The large value outliers in box plots, if any, are larger than the 3rd quartile + 1.5 * the interquartile range. The small value outliers in box plots, if any, are smaller than the 1st quartile – 1.5* the interquartile range. 10. Be able to identify likely outliers in a density plot and outliers by their representation in a box plot. 11. Be able to assess simple cases of skewness in box plots and be able to compare the medians of two box plots. ...
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This note was uploaded on 12/20/2011 for the course STAT 344 taught by Professor Staff during the Spring '08 term at George Mason.
 Spring '08
 Staff

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