# Beta (portfolio)

That is a simple but potentially usefull formula - which is not in the secret sauce Beta§ = wA * Beta(A) + wB * Beta(B) with P, a portfolio made up with wA of asset A and wB of asset B (wA + wB =1).

Another useful staff in tjis topic COV (A,B) = beta(A)*beta(B)*VAR(market) Yesterday couldn’t remind it…

SerGrey Wrote: ------------------------------------------------------- > Another useful staff in tjis topic > > COV (A,B) = beta(A)*beta(B)*VAR(market) > > Yesterday couldn’t remind it… For the market model at least. Dues this apply to other models also? Also for the market model, E(Ri) = Alpha + (Beta (i) x E(Rm)) Cov(i,m) = (Beta sq (i)) xVarM + Var(Residual(i))

allépourpêcher Wrote: ------------------------------------------------------- > Cov(i,m) = (Beta sq (i)) xVarM + Var(Residual(i)) I think you have a mistake here Var(i) = (Beta sq (i)) x VarM + Var(Residual(i)) But Cov(i,m) = Beta (i) * VarM … Do the all others agree?

^^ sergrey - you are right

You’re right. Typo there - should read: Var(Ri) = (Beta sq (i)) xVarM + Var(Residual(i))