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Displaying Data Using Graphs. Distribution Shapes and Characteristics Unimodal Distribution When histogram only shows one prominent peak Bimodal Distribution When there are two prominent peaks observed. Constructing histograms.
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Displaying Data Using Graphs • Distribution Shapes and Characteristics • Unimodal Distribution • When histogram only shows one prominent peak • Bimodal Distribution • When there are two prominent peaks observed
Constructing histograms • Select the number of classes you wish to fit your data to (between 7 and 15) • Based on number of observations • The greater the number of observations the greater the number of classes • For less than 15 observations, it makes no sense to construct a histogram • Figure out the range of data values that need to be plotted on the histogram • Highest – lowest value • Divide the number of classes you chose into the data range • Round this value up to an even number • The resulting number is your CLASS WIDTH • Determine the specific class boundaries • Count the number of observations in each class (Frequency table) • Draw the histogram
Displaying Data Using Graphs • 3. Stemplots (Stem and leaf diagrams) • Shape of values • Range • Variation • Outliers
Constructing Stemplots • Order observations from lowest to highest (optional) • Separate each observation into a stem that consists of all but the final digit; and leaf, the final digit • The goal is to use the first few digits in each number as the stem, in such a way that about 6 to 15 numbers are lined up vertically. • Attach the leaves to represent each data point • The next digit in the number not used as stem is used as leaf • The remaining digits are dropped