Legume germination

This diagram shows graphically a model for three factors with no interaction.

Initially the diagram shows only the mean response. Use the checkboxes to fit models with different combinations of factors.

Note how the diagram displays the two levels of Fungacide with a green and a purple grid when its main effect is in the model.

Click the y-x and y-z buttons to rotate. The parallel lines reflect the additive nature of the no-interaction model.

Note that the residuals for Alfalfa on Clay soils are large for the model with all main effects. Mention that this could be caused by...

A greenhouse experiment was conducted to determine the rate of emergence of seeds of three species of legumes, treated and not treated with a fungicide, and planted in three soil types. The response is the number of plants emerging out of 300 seeds.

  No fungicide   Fungicide
Legume species Silt loam Sand Clay   Silt loam Sand Clay
Alfalfa 266 286 66   276 271 215
Red clover 252 298 167   275 292 203
Sweet clover 152 197 52   178 219 121