Chapter_7_Exploring_Bivariate_Data.pdf

Chapter_7_Exploring_Bivariate_Data.pdf - SQQS1033 Data...

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SQQS1033 Data Exploratory and Generalisation lyf Nov’1 4 Page 1 Chapter 7 Exploring Bivariate Data Introduction From chapter 2 chapter 4, we learned how to graphically display and numerically describe sample data for one variable. Expand these techniques to cover sample data that involve two paired variables . For example: the relationship between age of an employee and his/her seniority in the company (Figure 7.1). Bivariate data - The values of two different variables that are obtained from the same population element. Each of the two variables may be either quantitative or qualitative. Three combinations of variable types can form by bivariate data: Both variables are qualitative Multiple bar chart One variable is qualitative and the other is quantitative Side by side box-plot Both variables are quantitative Scatter plot Scatter Plot A plot of all the ordered pairs ( x , y ) of bivariate data on a coordinate axis system. The input variable (independent variable), x , is plotted on the horizontal axis, and the output variable (dependent variable), y , is plotted on the vertical axis. Ordered one value, x , is always written first. Paired for each x value, there is corresponding y value from the same source. A scatter plot is a visual way to show the relationship between two quantitative variables . For example: If x is height and y is weight, then a height value and a corresponding weight value are recorded for each person.

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SQQS1033 Data Exploratory and Generalisation lyf Nov’1 4 Page 2 Figure 7.1 Example of scatter plot Describing the Pattern in a Scatter Plot For the distribution of a single quantitative variable , “ shape, center and spread ” is a useful summary. For bivariate quantitative data , the summary becomes “ shape, trend and strength ”. In describing a scatter plot, be sure to cover the following: Case and variables (what exactly does each point represent?) Shape Linearity: Is the pattern linear (scattered about a line) or curved? Cluster: Is there just one cluster, or is there more than one?
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• Spring '16
• Covariance and correlation, Non-parametric statistics, Spearman's rank correlation coefficient, SQQS1033 Data Exploratory

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