Shrimp culture
This example presents a data set for which the no-interaction model does not fit well.
Click the top three checkboxes to fit the main effects for the factors. Weight gain appears to be highest at 25% salinity, density 80 shrimps per litre and 35°C.
Mention that some residuals are very large for the model without interaction. Add a Temperature-by-salinity interaction to the model. The effect of changes to salinity is different at the different temperatures.
Commercial cultivation of the Californian brown shrimp was being planned, so scientists conducted a factorial experiment to assess how shrimp growth was affected by temperature, salinity and the density of shrimps in the tanks. The table below shows the average 4-week gain in weight per shrimp (mg) from the post-larval stage for each combination of factor levels.
80 shrimps/litre | 160 shrimps/litre | ||||
---|---|---|---|---|---|
Salinity | 25°C | 35°C | 25°C | 35°C | |
10% | 73 | 349 | 86 | 364 | |
25% | 482 | 330 | 208 | 316 | |
40% | 397 | 205 | 243 | 281 |