ch4 - Ch 4 GraphicalandNumerical DescriptiveTechniquesfor...

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1 Ch 4 Graphical and Numerical  Descriptive Techniques for  Bivariate Data  So far we have looked at one variable (univariate data) and their  descriptive statistics, i.e.  graphical summaries  and  numerical techniques . We now turn to bivariate data. The most important graphical  summary are:  - contingency table  - scatter diagram
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2 A newspaper readership survey sampled 352 newspaper readers and asked  which newspaper they read: Globe and Mail [1], Post [2], Star [3], or Sun [4]; and also asked then to indicate whether they were: Blue-collar worker [1]; White-collar worker [2], or professionals [3].  This reader’s response is captured  as part of the total number on the  contingency table (also called a  cross-classification table or cross- tabulation table is used to describe  the relationship between  two   nominal  variables.) contingency table  lists the frequency of each  combination of the values of the two  variables.
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3 Interpretation: The relative frequencies in the columns 2 & 3 are  similar, but there are large differences between columns 1 and  2 and between columns 1 and 3. dissimilar similar This tells us that blue collar workers tend to read different  newspapers from both white collar workers and professionals  and that white collar and professionals are quite similar in their  newspaper choice.
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4 We can also graph the relationship between two  nominal variables: Professionals tend  to read the Globe &  Mail more than  twice as often as the  Star or Sun…
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5 Graphing the Relationship Between Two  Cardinal  Variables Moving from nominal data to cardinal data, we are frequently  interested in how two cardinal variables are related. To explore this relationship, we often employ a  scatter diagram which plots two variables against one another. The  independent   variable is labeled X and is usually placed on  the horizontal axis, while the other,  dependent  variable, Y, is  mapped to the vertical axis. As an example, using data on the selling price of a home and its  size we can set the independent variable X as house size and  the dependent variable Y as the selling price. Then use Excel  to create a “scatter diagram.”
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6 It appears that in fact there is a relationship, that is, the greater  the house size the greater the selling price… Size of house Price
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ch4 - Ch 4 GraphicalandNumerical DescriptiveTechniquesfor...

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