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All five dvds with both guides
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Decisions Through Data Home


Statistics: Decisions Through Data

UNIT 3: Histograms and Distributions

Summary of the Video


Raul Lopez and his associates are studying the time pattern of lightning in Colorado. There is a vast amount of data. We look at the distribution of the time of the first lightning flash each day. Make a histogram : divide the day into hours, count the number of first flashes in each hour, and draw the graph. Then inspect the resulting distribution: there is symmetry and little spread, a surprising regularity that leads to an understanding of how electrical storms start in this part of the country. Then we look at the distribution of the time of the maximum number of flashes. Now there are outliers that point to days with unusual weather conditions.

The video uses graphics to briefly show how to make a histogram, with emphasis on how to choose the classes. The example of graphing the number of cars passing a school shows that classes are a matter for judgment. Too few or too many give an uninformative picture.

Finally, more on the overall patterns of distributions. The weekly wages of a group of workers illustrates strong skewness.