Correlations

The correlation matrix for Log-transformed sales by Fuel efficiency. — Figure 1. Correlation matrix for Log-transformed sales by Fuel efficiency

After removing the outlier and looking at the log-transformed sales, the correlation is now positive but still not significantly different from 0.

However, the customer demographics for trucks and automobiles are different, and the reasons for buying a truck or a car may not be the same. It's worthwhile to look at another scatterplot, this time marking trucks and autos separately.

To produce a scatterplot of Log-transformed sales by Fuel efficiency, controlling for Vehicle type, recall the Chart Builder.
Figure 2. Chart Builder
Select Grouped Scatter.
Select Log-transformed sales as the y variable.
Select Vehicle type as the variable to set colors by.
Click OK.

Scatterplot for Log-transformed sales by Fuel efficiency. There are two distinct clouds, one corresponding to cars, and one corresponding to trucks. There is a clear positive slope to the cloud of points corresponding to cars, and no clear shape to the cloud corresponding to trucks. — Figure 3. Scatterplot for Log-transformed sales by Fuel efficiency

The scatterplot shows that trucks and automobiles form distinctly different groups. By splitting the data file according to Vehicle type, you might get a more accurate view of the association. Also note that following the log-transformation of sales, the potential outlier in the upper left has disappeared.