__Notes__:

- An
**outlier**is often an extreme value in the response variable. One can often observe its existence as a large or small value in the residual plot. - An
**influential observation**is often an extreme value in the explanatory variable. - An observation is considered
**an influential observation**if it’s effect is to pull the regression line towards it. Consequently it’s existence will not show up in a residual plot.

** One observation’s inclusion or exclusion from the regression **should not **change the fit of the regression line dramatically.