I'm not exactly sure what type of evidence you are looking for with respect to the assertion that auditing a paper ballot system is easier than auditing a elect

I'm not exactly sure what type of evidence you are looking for with respect to the assertion that auditing a paper ballot system is easier than auditing a electronic voting system. Auditing a paper ballot system is trivial: any person who can see and can count can do it. On the other hand, if you are relying on a software system you need to audit the hardware, the software, etc, etc which requires a lot of skill and is tricky.