Ch5 Quantitative Data, Displaying and Describing.pdf

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University of Maryland
Business and Management
BMGT 230
Kazim Ruhi

Ch5 Quantitative Data, Displaying and Describing Friday,February 7,2014 11:56 AM Two graphs: histogram & stem-and-leaf plot note for steam-and-leaf plot • left side: bins,right side: "bars" • bars can be 0.0-0.5,do not have to always be 1 Building a Frequency Table:▯ Continuous Data 1. Determine the number of categories (classes/bins) a. General Guidelines 2. Establish class width a. Minimum width is the range of the data i. Largest data point–Smallest data point = Range 3. Set the class boundaries 4. Determine the frequency in each class a. Count the number of data points in each category Frequency Histogram -Visual representation of the frequency table • The classes/intervals/bins are shown on the horizontal axis • Frequency is measured on the vertical axis Example: 12,13,17,21,24,24,26,27,27,30,32,35,37,38,41,43,44,46,53,58 5. Sort raw data from low to high (already done) 6. Find range: 58-12 = 46 7. Select number of classes: 5 (usually between 5 and 20) 8. Compute class width: 10 (46/5 then round off) 9. Determine class boundaries: 10,20,30,40,50 10. Count the number of values in each class ▯ ▯ Shape of a distribution Mode: usually the single,most frequent value • one hump: unimodal • two humps: bimodal • three or more humps: multimodal • a distribution does not seem to have any mode,all bars approximately same height: uniform Symmetry • symmetric: mirror image • tails: the thinner ends of a distribution • skewed: one tail stretches out farther than the other Outlier -Data points that don’t seem to fit in the distribution. • They should be understood in the context of the data.An outlier for a year of data may not be an outlier for the month in which it occurred and vice versa. • They should be investigated to determine if they are in error.The values may have simply been entered incorrectly.If a value
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