Once you determine that a straight-line relationship exists between a dependent variable Y and the independent variable X, you need to find the straight line that is the best fit to the data. Two values define any straight line: the Y intercept and the slope.

The Y
intercept is the value of Y when X = 0, represented by the symbol b_{0}. The **slope** is the change in Y per unit change in X represented by the symbol b_{1}. A positive slope means Y increases as X increases. A negative slope means Y decreases as X increases. Figure 9.2 illustrates the Y intercept and the slope.

You use the Y intercept and the slope to develop the prediction ...

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