code class$=$"asciimath"$>$lnQ $=\backslash$alpha $+\backslash$beta $1$ ln P $+\backslash$beta $2$ ln M $+\backslash$beta $3$ ln S$+\backslash$epsi In estimating the demand function for a good X$,$ a researcher collected data on various households' consumption of good X for various price levels. The researcher also colected data on household income $($M$)$ and household size $($S$).$ Mathematically, the regression equation is : lnQ $=\backslash$alpha $+\backslash$beta $1$ ln P $+\backslash$beta $2$ ln M $+\backslash$beta $3$ ln S$+\backslash$epsi $,$ where P is the price per unit of X and Q is the quanity consumed. what is the interpretation of beta $1?$