\BeginKnitrBlock{exercise}\iffalse{-91-80-114-111-120-121-32-109-101-97-115-117-114-101-109-101-110-116-115-93-}\fi{}<div class="exercise"><span class="exercise" id="exr:unnamed-chunk-16"><strong>(\#exr:unnamed-chunk-16)  \iffalse (Proxy measurements) \fi{} </strong></span>What are some examples of proxy measurements you will use in your own research? What are their limitations?</div>\EndKnitrBlock{exercise}