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Fitting Curves |

Open the MININGX data set. |

Choose Analyze:Fit ( Y X ). |

The fit variables dialog appears, as shown in Figure 13.3.

Select the variable DRILTIME, then click the Y button. |

**DRILTIME** appears in the **Y** variables list.

Select the variable DEPTH, then click the X button. |

**DEPTH** appears in the **X** variables list.

Click the Output button. |

The fit output options dialog, shown in Figure 13.4,
appears on your display.

In the output options dialog, you specify which curves and tables will appear in the fit window. The default curve is a polynomial of degree one, that is, a line. The options set by default in this dialog are appropriate aids to a careful modeling of the data. They are not needed here where the purpose is to produce a visual display that reflects the trend of the data.

Turn off all check boxes by clicking on any that are highlighted. |

Click the OK button in all dialogs. |

A fit window appears, as shown in Figure 13.5.

The fit window contains a plot of **DRILTIME** by
**DEPTH** along with a table summarizing the fit.
A simple regression line is superimposed on the plot;
it follows the *linear* trend of the data.
Notice, though, that the plot shows curvature
that a straight line cannot follow.
First examine the **Parametric Regression Fit** table corresponding
to these data.
The **R-Square** value is **0.5802**, which means that 58% of the variation
in drilling times is explained by **DEPTH**.
The rest of this table contains statistics pertinent to hypothesis
testing, and they are discussed in Chapter 14, "Multiple Regression."

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