Avoiding performance bias: blinding of patients

You are probably familiar with the term "double-blind"; but how can we tell double-blind from "single-blind", or even triple blind?

It's easiest to think in terms of "what happens" during a trial, and progress from there. Performance bias can arise if the patients in one group are treated differently from those in the other group in any way apart from the experimental treatment itself. Unfortunately, there are many ways in which this could happen.

Imagine our trial of "apples for the common cold". Which kinds of participant in the study could be in a position to influence the results? TYPE YOUR ANSWER IN THE BOX BELOW: