in our company there started a discussion about different ways feedback should be presented inline - so in a textbox-style below, or as a popup/modal, as it is now.
We have exchanged different arguments like
contra inline: 1) too much text. 2) they would not read it. 3) The modal shows the feedback in a focused way.
contra popup: 1) with a modal you do not see your answers anymore. 2) You get "ripped" out of the quiz.
As both sides have pros/cons (surely more than the ones above) we asked if anyone has conducted any usability studies, so we have "data" and not only "opinions"?
I would be happy to hear from any data / research / findings, which could help us in our elaborated decision.