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