which is a function of r2$ explain how an autoregressive model can be used? why not look at R in an autoregressive model? what does $r measure in regression why is r2$ used in a autoregressive model why don't we look at $r2$ when fitting an autoregressive model? why doesn't regression models use regressive models? how does autoregressive model work why do we don't look at r in regression why don't we measure the variance of an autoregressive model why do we not use r2$ for regression? why do not we look at $r2$ when fitting a linear regression? why don't we look at $r when fitting an autoregressive model why don't we look at $r why are the autoregressive models used what is regressive model why don't we look at $r2$ in an autoregressive modeling why do we not look at r2$ when fitting an autoregressive model? why don't we look at r$ when fitting an autoregressive model? why don't we look at r2$ when fitting a linear model?