But for the average person, perception does influence how likely they are themselves to take part in corruption, and that in turn does influence the total amoun

But for the average person, perception does influence how likely they are themselves to take part in corruption, and that in turn does influence the total amount of corruption in a country. Actual corruption is very hard to measure, so perception of corruption is a reasonable thing to research since it is in many ways "the best you can do" to get some measure of actual corruption.