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Decisions Through Data Home


Statistics: Decisions Through Data

UNIT 2: Stemplots

Summary of the Video

The video first introduces the idea of a variable , any numerical quantity that takes different values for different people or things. The distribution of a variable is the pattern of values. We see Army basic training and the Army's task of outfitting its soldiers, who are quite different than in the past. The Army measures many variables on a large sample of soldiers to gain information about the distribution of, for example, head sizes.

A graph is usually the first step in describing data. Then we learn how to look at a stemplot. First look for the overall pattern . It is quite regular and roughly symmetric . There is a single peak close to the center. We also look at how spread out the data are.

Now we visit TV Channel 38 in Boston as its executives decide which programs to show. Data about what kind of audience each show draws is essential. We look at a stemplot of the ages of people who watch an action-adventure series. The data are in tenths of a year, so we truncate by removing the tenths before making a stemplot. There's an outlier , a joker who claimed to be 120 years old. After looking for the overall pattern of a distribution, look for striking deviations from the pattern, such as outliers. The show draws a young audience, so the station will position it opposite shows on other stations that attract older audiences.


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