\BeginKnitrBlock{exercise}\iffalse{-91-84-121-112-101-115-32-111-102-32-101-114-114-111-114-32-98-97-114-115-93-}\fi{}<div class="exercise"><span class="exercise" id="exr:unnamed-chunk-64"><strong>(\#exr:unnamed-chunk-64)  \iffalse (Types of error bars) \fi{} </strong></span>Often you see plots with error bars around the sample mean of the data. What is the true (error free) value in this case?</div>\EndKnitrBlock{exercise}