Vitamin B and weight gain of rats over 4 weeks
The standard deviation of the response is similar for different doses of vitamin B2, so a normal linear model with transformed explanatory variable may fit.
Drag the red line on the horizontal axis to apply a power transformation to the dose. A log transformation (between a power of 0.01 and -0.01) works well. (Use the arrow keys on the keyboard to make fine adjustments.)
This model implies a nonlinear relationship on the original axes (on the scatterplot on the right).
The data set was obtained from an experiment in which 18 rats were given diets containing different quantities of riboflavin (vitamin B2). The doses used in the experiment were 2.5, 5, 10 and 20 mug per day and the weight gains of the rats (grams) were recorded over a period of 4 weeks.
The relationship between weight gain and dose is nonlinear — weight gains seem to be less affected by increasing the dose once it is over 10 mug per day.