Differentiating between the interactions available for task EXPLAIN

The following question is addressed in this section: if you want to construct a test question which presents your candidates with an EXPLAIN task, how do you decide between the interactions available?  

The GUIDANCE differentiator

The main difference between the two interactions used for the task EXPLAIN lies in the ways in which it is possible to limit candidates' input when using the Text Entry interaction: it is possible (and common) to use Text Entry to provide a limited set of characters (such as numbers or math symbols when the question asks for a mathematical explanation, to reduce possible entry mistakes), and it is generally used for shorter texts than the Extended Text interaction.

The limitations placed on the candidates' responses in Text Entry interactions and, in contrast, the freedom of response in Extended Text interactions can be mapped quite clearly onto the differentiator indicating the amount of guidance given to them. 

Indeed, when we plot the two interaction types on the GUIDANCE spectrum as follows:

We can see that whereas Text Entry offers a little guidance, Extended Text offers none at all. This gives us the main indicator when choosing between these two interactions for a particular test question of the type EXPLAIN.

To sum up, the most important factor in choosing between the two main interactions for a particular test question of the type EXPLAIN will be the amount of guidance you wish to give candidates.