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Nonlinear Econometrics for Finance Final Exam - 2022
发布时间:2022-03-16
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Nonlinear Econometrics for Finance
Final Exam - 2022
Question 1
Consider three independent random variables xl , x2 and x3 with the same expected value µ and
variances 1/8, 1 and 4, respectively. Consider, also, two estimators l and
2 defined as
l =
x3 +
x2
and
2 = 2xl - x2 .
Choose the best answer:
A) Both l and
2 are unbiased for µ and they are equally efficient
B) Both l and
2 are unbiased for µ but
2 is more efficient
C) Both l and
2 are biased for µ
D) Both l and
2 are unbiased for µ but
3 = x2 is preferable to both
Question 2
Consider a population with mean µ and variance σ 2 < o. After collecting an IID sample of T ob- servations, you estimate the mean of the population with an estimator T such that E(
T ) = 0.5µ and V(
T ) =
σ . Which statement is correct?2
A) The estimator T is not consistent but 2
T is
B) The estimator T is consistent because its variance goes to zero
C) We cannot determine whether the estimator T is consistent with this information
D) The estimator 2 T is unbiased but inconsistent
Question 3
Consider the CCAPM model and the following equation for the price of an asset in equilibrium:
pt = Ct(mt+l, xt+l) + Et(xt+l),
where pt is the price of the asset at time t; xt+l is the payoff of the asset at time t + 1; Rf indicates the return on the risk-free asset; mt+l is the stochastic discount factor; and Et and Ct denote the conditional expectation and the conditional covariance given time-t information, respectively.
Which of the following is true?
A) The asset sells at a discount and the covariance term in the equation above is negative
B) The asset sells at a discount and the covariance term in the equation above is negative if the asset gives a high payoff when consumption is low
C) The asset sells at a discount and the covariance term in the equation above is negative if the asset gives a high payoff when consumption is high
D) The asset sells at a discount and the covariance term in the equation above is positive if the asset gives a high payoff when consumption is high
Question 4
We want to estimate the probability that a market index will go up in the next week. As a first attempt, we collect a large sample of weekly data on the index r0 , rl, r2 , ..., rT and we record xt = 1 if rt - rt − l > 0 and xt = 0 otherwise. Assume that it is reasonable to think of this sample as an IID sample. Using our sample xl, x2 , ...., xT , we estimate the probability that the index goes up using a sample proportion:
T
=
xt .
t=l
We know that the variance of is V(
) = p(1 - p)/T. A reasonable estimator for this variance is
(
) =
(1 -
)
Choose the best answer:
A) (
) is consistent and unbiased for V(
)
B) (
) is consistent but not unbiased for V(
)
C) (
) is not consistent (since it goes to zero) but is unbiased for V(
)
D) (
) is neither consistent (since it goes to zero) nor unbiased for V(
)
Question 5
Suppose you have a sample of T observations from a normally distributed random variable X ~ N (µ, σ2 ). You are interested in estimating the mean of the population µ but, instead of using the sample mean X =
Xt as your estimator, you decide to use the sample median Xmed. After consulting a statistics book, you discover that
Xmed ~ N ╱µ, 1.5707 、 .
Choose the best asnwer:
A) The median Xmed is not a consistent estimator of µ
B) The median Xmed is as efficient as the mean X because its variance also goes to zero
C) The median Xmed can only be used to estimate the population median and should not be used to estimate µ
D) None of the above
Problem 1 (80 points)
Consider the following linear regression model:
Rt(e),i = αi + βiRt(e),m + εt,i ,
where Rt(e),i is the excess return on an asset i, Rt(e),m is the excess return on the market and εt,i is a standard shock with the following properties E[εt,i] = 0 and V[εt,i] = σε(2), for all assets i.
Notice that the model implies the CAPM if αi = 0 for all assets i. In fact:
E(R ,i) = αi + βiE(R ,m)
Please note: all the questions in Problem 1 are separate and can be tackled without solving previous questions.
1. (15 points.) What is the economic interpretation of αi?
2. (20 points.) The least-squares estimator of αi is i =
Rt(e),i -
i
Rt(e),m . Using
the Weak Law of Large Numbers and Slutsky’s theorem, show that
IT (i - αi) 二(d) N ╱0, ╱ 1 +
\ σε(2)\ , (1)
where µRù(μ) is the expected excess return on the market and σR(2)ù(μ) is the variance of the excess market return, using the fact that
IT (i - βi) 二(d) N ╱0,
\ .
3. (15 points.) Use the asymptotic distribution in Eq. (1) to test the hypothesis αi = 0. (Be as precise as possible.)
4. (10 points.) Consider, now, N assets, rather than one. Write the vector of N intercepts as
╱ α(α)2(l) 、
..αN(..). .
Also, denote by Σε the variance/covariance matrix of the vector ε, where
╱ εt,l 、
εt,N
We have
IT ( - α) 二(d) N ╱0, ╱ 1 +
\ Σε\ .
Discuss why Eq. (2) follows logically from Eq. (1).
(2)
5. (20 points.) Use Eq. (2) to construct a one-sided test of the hypothesis that the vector α is equal to zero.
Problem 2 (80 points)
In order to understand whether positive shocks to returns (induced by favorable aggregate news) have a different impact on variance than negative shocks to returns (induced by negative aggregate news), we run an asymmetric GARCH(1,1) model. We also allow for GARCH-in-mean effects:
rt = λht + εt ,
εt = ìhtut with ut ~ N (0, 1),
ht = α0 + αlht − l + α2 εt(2)− l+ α3 εt(2)− l 1{ε≥ − ≥<0} .
The conditional mean output:
ht
Estimate
3.3827
Std. error
1.1670
t-ratio
2.898
p-value
0.0037
The conditional variance output: |
|
|
|
|
|
Estimate |
Std. error |
t-ratio |
p-value |
Intercept |
1.74e - 06 |
1.38e - 07 |
12.66 |
0.000 |
εt(2)− l |
0.024722 |
0.004225 |
5.851 |
0.000 |
ht − l |
0.912771 |
0.003613 |
252.61 |
0.000 |
εt(2)− l 1{ε≥ − ≥<0} |
0.091709 |
0.004998 |
18.347 |
0.000 |
1. (10 points.) Test formally the hypothesis that α3 = 0 and interpret your results economically.
2. (10 points.) Test formally the hypothesis that λ is equal to 4.
3. (10 points.) Suppose that λ = 4 is a classical measurement of investors’ risk aversion. How
would you interpret economically the conditional mean of the model, i.e., Et − l(rt) = λht?
4. (10 points.) If λ = 4, what is the conditional distribution of rt given ht = .0000314?
5. (20 points.) The last return in the sample is -0.0045 and the value of hT associated with the last observation in the sample is .0000314. Write the one-day ahead forecast of the variance for time T + 1 (i.e., the one-day ahead out-of-sample forecast).
6. (10 points.) Use your result from Point 5 to find the one-day ahead 1% Value at Risk on a million dollar investment in the S&P500 index.
7. (10 points.) If ht −2 increases by a specific amount δ, what is the impact on ht?
Problem 3 (80 points)
A bank wants to predict the probability that a borrower will repay a loan. The bank has data on previous borrowers that can be used to estimate a model for the probability of repayment. Let xi = (xli, x2i, ..., xKi ) be a 1 x K vector containing some demographic characteristics of borrower i, such as income, current debt, employment status, gender, race, location, etc. The bank knows for each borrower i in the sample whether she/he repaid her/his loan (yi = 1) or not (yi = 0). The repayment probability is modeled according to a logistic regression model in which the probability that the borrower is repaid is
ex ﹔β
P (yi = 1|xi; β) = p(xi; β) =
where β = (βl, β2 , ..., βK )T is a K x 1 vector of parameters to estimate. Suppose the bank has a database with an IID sample of n borrowers, so the data are
yi, xi for i = 1, ..., n.
Given this information, please answer the following questions.
1. (25 points.) Write the likelihood of the model.
2. (25 points.) Show that the standardized log-likelihood can be written as log L({x}, β) =
╱ i l
yixiβ - log ╱ i
l ì 1 + ex ﹔β/\\ .
3. (30 points.) Show that the ML estimates n can be obtained by solving the following system of equations:
(yi - p(xi; β)) xki = 0 for k = 1, ..., K.
Problem 4 (80 points)
Consider the following model for the short-term interest rate:
drt = α0 dt + γ0dBt ,
where drt is the continuous-time change in the interest rate, Bt is a Brownian motion and (α0 , γ0 ) are two parameters to estimate. We wish to estimate this model using GMM and, in order to do so, we discretize it in the following way:
rt+A ≥ - rt = α0 ∆t + γ0 εt+A ≥ ,
where the variable εt+A ≥ N (0, ∆t) is iid. Note that “discretizing” the model simply means going from “continuous-time” (dt) to “discrete-time” (∆t) which is more consistent with the way in which data is sampled.
1. (25 points.) Using the discretized model, compute Et[rt+A ≥ - rt] and Vt[rt+A ≥ - rt].
2. (30 points.) Use the results in Point 1. to derive two moment conditions to be used for the estimation of the model parameters. What are Γ0 and Φ0 for this model?
3. (25 points.) Suppose that your model contains another parameter, γl:
drt = α0 dt + γ0rt(γ)≥ dBt .
Modify the previous discretized model to obtain a new discretized model (with three param- eters, i.e., α0 , γ0 and γl) and derive 3 moment conditions to estimate the three parameters. Hint: use rtVt[(rt+A ≥ - rt)] to derive the third moment condition.
Problem 5 (80 points)
Consider the following regression model:
yi = α + xi(β) + εi ,
with E[εi|xi] = 0.
1. (30 points.) Compute E[εixi|xi]. Using this result, write two moment conditions which can be used to estimate α and β by GMM.
2. (30 points.) What is the 2 x 2 matrix Γ0 for this model? (Be as precise as possible.)
3. (20 points.) What is the 2 x 2 matrix Φ0 for this model? (Be as precise as possible.)