Complex sentence: For example, if one is examining the relationship among four variables, and the model of best fit contained one of the three-way interactions, one would examine its simple two-way interactions at different levels of the third variable.
Split into simpler sentences: For example, if was examining the relationship among four variables, and the model of best fit contained one of the three-way interactions. You would examine its simple two-way interactions at different levels of the third variable.