Studying the impact of intensity is important but complicated.

This commentary suggests that the most commonly studied aspect intensity (dose frequency) on overall rate of response to treatment may often be weak or conditional. To improve statistical power of tests of weak effects additive statistical models have typically been used. However, multiplicative models may be a more productive route to understanding dose frequency effects on children's speech and language development. To illustrate, recent findings are presented that dose frequency effects on vocabulary development varied by two child characteristics. Finally, it is suggested that spacing of teaching episodes within an intervention session be included as a variable in the multi-dimensional model of treatment intensity. Spacing teaching episodes may eventually prove to be one of the more powerful aspects of intensity.