Example of editing scale transformations
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You are a vintner concerned about the cost of lab work done to measure sugar content in your grapes. A field test that can be done quickly at a lower cost seems promising. You hope a regression analysis will provide an equation to predict the precise reading, so you plot the readings against one another, using a scale transformation on the response variable to find an appropriate model.

Step 1: Create the graph

1    Open the worksheet SUGAR.MTW

2    Choose Graph > Scatterplot > choose With Regression > OK.

3    In Y, enter Field. In X, enter Lab. Click OK.

Graph window output

Step 2: Edit the transformation

1    Double-click the x-scale.

2    Click the Transform tab.

3    Under Transformation, choose Logarithm.

4    Under Base, choose 10. Click OK.

Graph window output

Interpreting the results

In the initial graph, it is clear that a regression fit is not appropriate with the original data. This pattern indicates that a transformation might be useful. A regression plot utilizing a log transformation of the response variable and a linear regression model would be most appropriate to find an equation for predicting lab results from in-field refractometer readings.