\BeginKnitrBlock{exercise}\iffalse{-91-65-32-108-105-110-101-97-114-32-109-111-100-101-108-32-119-105-116-104-32-116-119-111-32-108-101-118-101-108-115-32-105-110-32-116-104-101-32-112-114-101-100-105-99-116-111-114-93-}\fi{}<div class="exercise"><span class="exercise" id="exr:unnamed-chunk-113"><strong>(\#exr:unnamed-chunk-113)  \iffalse (A linear model with two levels in the predictor) \fi{} </strong></span>IMPORTANT!! Do you think it's possible to write down a similar linear model when we only want to compare two groups?! What would happen?</div>\EndKnitrBlock{exercise}