. Let X and Y be random variables. The conditional
variance of Y given X, denoted Var(Y | X),
is defined as
Var(Y | X) = E[Y
2
| X] − E[Y | X]
2
.
Show that Var(Y ) = E[Var(Y | X)] + Var(E[Y | X]). (This equality
you are showing is known
as the Law of Total Variance). Hint: From the Law of Total
Expectation, you get Var(Y ) =
E[Y
2
] − E[Y ]
2 = E
h
E[Y
2
| X]
i
− E
h
E[Y | X]
i2
.
Homework Answers
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. Let X and Y be random variables. The conditional
variance of Y given X, denoted...
For random variables X and Y with finite variance, the law of total variance states that...
For random variables X and Y with finite variance, the law of total variance states that Var(X) E(Var(X|Y)) + Var(E(XTY)) variance analogue of E Write out a formula that For each n, let Varn be the conditional relates two such conditional variances as the formula for the iteration condition relates two conditional expectations
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O RANDOM VARIABLES AND DISTRIBUTIONS Expectation and variance of a random variable Let X be a random variable with the following probability distribution: Value x of X P(X-) 0.35 0.40 0.10 0.15 10 0 10 20 Find the expectation E (X) and variance Var(X) of X. (If necessary, consult a list of formulas.) Var(x) -
The conditional variance of X, given Y, is defined by Prove the conditional variance formula, namely,...
The conditional variance of X, given Y, is defined by Prove the conditional variance formula, namely, Var(X) E[Var(X|Y)] Var(E[XYl) Use this to obtain Var(X) in Example 1 S(B) and check your result by differentiating the generating function
The random variables X and Y have the joint PDF fx,y(x,y)=0.5, if x>0 and y>0 and...
The random variables X and Y have the joint PDF fx,y(x,y)=0.5, if x>0 and y>0 and xtys2, and 0 otherwise. Let A be the event Ys1) and let B be the event (Y>X). (You can use rational numbers like 3/5 for your answers.) 1. Calculate P(BIA). 2. Calculate fxıy(xlO.9) fxIY(0.39820710.9) 3. Calculate the conditional expectation of X, given that Y=1.8 4, Calculate the conditional variance of X, given that Y=1.4 5. Calculate fxlB(x) fXIB(0.11) 6. Calculate E[XY]. 7. Calculate the...
MA2500/18 Section B (Answer THREE questions) 6. Let X and Y be jointly continuous random variables...
MA2500/18 Section B (Answer THREE questions) 6. Let X and Y be jointly continuous random variables defined on the same prob- ability space, let fx.y denote their joint PDF, and let fx and fy respectively denote their marginal PDFs (a) Let z be a fixed value such that fx(x) >0. Write down expressions for 12] (i) the conditional PDF of Y given X = z, and (i) the conditional expectation of Y given X (b) State and prove the law...
X and Y are random variables (a) Show that E(X)=E(B(X|Y)). (b) If P((X x, Y )...
X and Y are random variables (a) Show that E(X)=E(B(X|Y)). (b) If P((X x, Y ) P((X x})P({Y y)) then show that E(XY) = E(X)E(Y), i.e. if two random variables are independent, then show that they are uncorrelated. Is the reverse true? Prove or disprove (c) The moment generating function of a random variable Z is defined as ΨΖφ : Eez) Now if X and Y are independent random variables then show that Also, if ΨΧ(t)-(λ- (d) Show the conditional...
(3) 18 pts] Let Ya and Y, denote Bernoulli random variables from two different populations, denoted...
(3) 18 pts] Let Ya and Y, denote Bernoulli random variables from two different populations, denoted a and b. Suppose that E(%)-Pa and E(%)-pb. A random sample of size na is chosen from population a, with sample average denoted pa, and a random sample of size nb is chosen from population b, with sample average denoted Suppose the sample from population a is independent of the sample from population b. (a) Show that E(Pi) P and var(P) p pi)/n, for...
Given random variables X1, X2, Y with E[Y | X1, X2] = 5X1 + X1X2 and...
Given random variables X1, X2, Y with E[Y | X1, X2] =
5X1 + X1X2 and E[Y
2
| X1, X2] =
25X2
1X2
2 + 15, find
E[(X1Y + X2)
2
| X1, X2].
ㄨ竺Bin(2.1/4). Suppose X and Y are independent random variables. Find the expected value of YX. Hnt: Consider conditioning on the events (X-j)oj0,1,2. 9. Given random variables XI,X2, Y with E'Y | XiN;|-5X1 + X1X2 and Ep2 1 X1,X2] 25XX15, find 10. Let X and Y...
1. Let X and Y b e random variables, with μΧ = E(X), μΥ = E(Y),...
1. Let X and Y b e random variables, with μΧ = E(X), μΥ = E(Y), σ炙= Var(X) and σ Var(Y) (2) Let Ỹ be a linear function of X, ie. Ỹ = +51X where bo and bl are fixed real numbers. We want to minimize the discrepancy of Y from Y, i.e. minimizing the quantity (a) Find the values of bo and bi that minimizes Q (b) Use (a) to show that the minimal value of Q is σ....
(3) 18 pts] Let Ya and Y, denote Bernoulli random variables from two different populations, denoted...
(3) 18 pts] Let Ya and Y, denote Bernoulli random variables from two different populations, denoted a and b. Suppose that E(%)-Pa and E(%)-pb. A random sample of size na is chosen from population a, with sample average denoted pa, and a random sample of size nb is chosen from population b, with sample average denoted Suppose the sample from population a is independent of the sample from population b (a) Show that E(Pi) Pi and var(Pi)-P( pi)/n, for j...
For random variables X and Y with finite variance, the law of total variance states that Var(X) E(Var(X|Y)) + Var(E(XTY)) variance analogue of E Write out a formula that For each n, let Varn be the conditional relates two such conditional variances as the formula for the iteration condition relates two conditional expectations
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The conditional variance of X, given Y, is defined by Prove the conditional variance formula, namely, Var(X) E[Var(X|Y)] Var(E[XYl) Use this to obtain Var(X) in Example 1 S(B) and check your result by differentiating the generating function
The random variables X and Y have the joint PDF fx,y(x,y)=0.5, if x>0 and y>0 and xtys2, and 0 otherwise. Let A be the event Ys1) and let B be the event (Y>X). (You can use rational numbers like 3/5 for your answers.) 1. Calculate P(BIA). 2. Calculate fxıy(xlO.9) fxIY(0.39820710.9) 3. Calculate the conditional expectation of X, given that Y=1.8 4, Calculate the conditional variance of X, given that Y=1.4 5. Calculate fxlB(x) fXIB(0.11) 6. Calculate E[XY]. 7. Calculate the...
MA2500/18 Section B (Answer THREE questions) 6. Let X and Y be jointly continuous random variables defined on the same prob- ability space, let fx.y denote their joint PDF, and let fx and fy respectively denote their marginal PDFs (a) Let z be a fixed value such that fx(x) >0. Write down expressions for 12] (i) the conditional PDF of Y given X = z, and (i) the conditional expectation of Y given X (b) State and prove the law...
X and Y are random variables (a) Show that E(X)=E(B(X|Y)). (b) If P((X x, Y ) P((X x})P({Y y)) then show that E(XY) = E(X)E(Y), i.e. if two random variables are independent, then show that they are uncorrelated. Is the reverse true? Prove or disprove (c) The moment generating function of a random variable Z is defined as ΨΖφ : Eez) Now if X and Y are independent random variables then show that Also, if ΨΧ(t)-(λ- (d) Show the conditional...
(3) 18 pts] Let Ya and Y, denote Bernoulli random variables from two different populations, denoted a and b. Suppose that E(%)-Pa and E(%)-pb. A random sample of size na is chosen from population a, with sample average denoted pa, and a random sample of size nb is chosen from population b, with sample average denoted Suppose the sample from population a is independent of the sample from population b. (a) Show that E(Pi) P and var(P) p pi)/n, for...
Given random variables X1, X2, Y with E[Y | X1, X2] =
5X1 + X1X2 and E[Y
2
| X1, X2] =
25X2
1X2
2 + 15, find
E[(X1Y + X2)
2
| X1, X2].
ㄨ竺Bin(2.1/4). Suppose X and Y are independent random variables. Find the expected value of YX. Hnt: Consider conditioning on the events (X-j)oj0,1,2. 9. Given random variables XI,X2, Y with E'Y | XiN;|-5X1 + X1X2 and Ep2 1 X1,X2] 25XX15, find 10. Let X and Y...
1. Let X and Y b e random variables, with μΧ = E(X), μΥ = E(Y), σ炙= Var(X) and σ Var(Y) (2) Let Ỹ be a linear function of X, ie. Ỹ = +51X where bo and bl are fixed real numbers. We want to minimize the discrepancy of Y from Y, i.e. minimizing the quantity (a) Find the values of bo and bi that minimizes Q (b) Use (a) to show that the minimal value of Q is σ....
(3) 18 pts] Let Ya and Y, denote Bernoulli random variables from two different populations, denoted a and b. Suppose that E(%)-Pa and E(%)-pb. A random sample of size na is chosen from population a, with sample average denoted pa, and a random sample of size nb is chosen from population b, with sample average denoted Suppose the sample from population a is independent of the sample from population b (a) Show that E(Pi) Pi and var(Pi)-P( pi)/n, for j...
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