4. No relationship between the variables, as shown in part (d) of Figure 2.6. Thebest-fit line is horizontal, with a slope of zero and, when we view the scatter diagram, knowing the value of x is of no help whatsoever in predicting the value of y.In this chapter, we will consider only linear relationships between variables, andthere will be two possibilities for fitting a straight line (i.e., a linear equation) to thedata. The first possibility is the “eyeball” method, using personal judgment and aruler applied to the scatter diagram. The second, more accurate, approach is to usethe computer and your statistical software to fit a straight line that is mathematicallyoptimum. This technique, known as the “least-squares” method, will be discussedin much more detail in Chapter 15, Simple Linear Regression and Correlation.
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