Lecture 5 Notes[1]

Lecture 5 Notes[1] - STAT 225 Lecture 5 Notes Scatter Plots...

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STAT 225 Lecture 5 Notes Scatter Plots and Trend lines Whenever we want to analyze two qualitative variables simultaneously we learned how to used cross- tabulations. Examining the relationship between two numeric variables graphically: When we have 2 quantitative variables and we want to look at the relationship between them, we look at a scatter plot. If the scatter plot looks linear, then we implement a least squares regression analysis or trend line analysis to get an equation of a line that uses x (Explanatory or Independent variable) to explain what happens with y (Response or Dependent variable). Ex. Storm Data is a publication of the National Climatic Data Center that contains a listing of tornadoes, thunderstorms, floods, lightning, temperature extremes, and other weather phenomena. Table 10.4 in text summarizes the annual number of tornadoes in the U.S. between 1953 and 2005. Investigate the linear relationship between Year and Number of Tornadoes.
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If a linear relationship between the two variables exists we eventually would like to be able to write down the equation corresponding to this relationship: y a x b    a is the slope of the line, i.e. rise a run b denotes the y-intercept of the line. It is easy to see that if we had such an equation we could easily make predictions for y given some particular value of x.
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Lecture 5 Notes[1] - STAT 225 Lecture 5 Notes Scatter Plots...

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