Hi John,
This can be done in a few ways. As you mention above, you could nest a series of if statements to evaluate whether 'yes' is selected. In this case, because you only need to identify the presence of one 'yes', I might suggest concatenating the questions together and using a regex to find the value 'yes' (or whatever the yes value is), and then using it in an if statement to set yes or no:
if(regex(concat(${q1}, ${q2}, ${q3}, ${q4}, ${q5}, ${q6}, ${q7}), '^.*yes.*$'), 'yes', 'no')