Simple view of reading ($R=DC$)

A model distinguishing decoding and linguistic comprehension as necessary contributors to reading comprehension. The product formulation motivates different profiles with similar aggregate performance, but does not license multiplying arbitrary raw test scores or treating the two components as indivisible mechanisms.^[ref]

In the idealised model $R=DC$, changing decoding by $h$ with comprehension fixed changes the product by $hC$, since $(D+h)C-DC=hC$. Similarly, changing comprehension by $k$ changes it by $kD$. ThusIf either component is zero, increasing only the other leaves the product zero. Equal products can arise from different profiles: $0.3\times 0.9=0.9\times 0.3=0.27$. These algebraic properties explain the model's complementarity; they are not estimates of treatment response or diagnostic cutoffs.