ECMT3150: Assignment 1 (Semester 1, 2023)
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ECMT3150: Assignment 1 (Semester 1, 2023)
Due: 5pm, 21 March 2023 (Tuesday)
1. [Total: 24 marks]
Note: Please append your R codes (as a separate .R file) for part (g) while you submit the assignment.
Let Xi denote the log-price of a stock, Cherry Inc. (code: CRRY), by the end of trading day i, and let AXi := Xi _ Xi━1; thus AXi is the log-return on trading day i (i.e., over period (i _ 1;i]).
Assume {Xi}≥〇 follows the AR(1) model:
(1)
where ui ~ iid normal with mean 0 and variance 72 .
Let {Fi}i≥〇 be the natural filtration generated by {ui}i≥〇 .
(a) [2 marks] Express AXi in terms of Xi━1 and ui .
(b) [2 marks] Compute E(AXi|Fi━1).
(c) [2 marks] Compute Var(AXi|Fi━1).
(d) [2 marks] What is the condition on o〇 and o1 such that {AXi}i≥1 is a martingale difference sequence?
A trading strategy is defined by {π i}i≥〇, where π i is measurable with respect to Fi . Specifi- cally, π i represents the number of CRRY shares a trader buys at the start of day i. The log-return due to the trading strategy over period (0;T] is given by
(e) [4 marks] Alice invested in a share of CRRY using a buy-and-hold strategy, with π i 三 1 for all i. Compute E(rT ) and Var(rT ) with o〇 = 0 and o1 = 1.
(f) [4 marks] Bob suggested another strategy, with π i 三 AXi for i > 0 and Compute E(rT ) and Var(rT ) with o〇 = 0 and o1 = 1.
(g) [8 marks] Carol suggested yet another strategy, with πi 三 1{AXi > 0} and π〇 = 1. We want to evaluate the risk-return tradeo§ of the proposed strategies using computer simulation.
Start an R session, and set a random seed equal to the last 3 digits of your student ID.1 Then generate B sample values of rT (name them as r ;r ;:::;rB)), and compute the sample mean and variance of rT as follows:
For the purpose of your simulations, set T = 63, 72 = 0:1, B = 1000.
The Sharpe ratio, deÖned as SR = ), is a common measure of the risk-return tradeo§. Trading strategies with higher SR are more preferred by investors.
Complete the following table with SR values. Comment on the performance of the trading strategies under di§erent scenarios.
o〇 |
o1 |
Alice |
Bob |
Carol |
0 |
1 |
|
|
|
0:01 |
1 |
|
|
|
_0:01 |
1 |
|
|
|
0 |
0:9 |
|
|
|
0 |
1:1 |
|
|
|
2. [Total: 16 marks] Let M denote the mood of Mimi (h: happy; a: angry), and let W denote the weather (s: sunny; r: rainy). The joint probability distribution of M and W is given in the table below. The row and column sums are displayed in the last column and in the last row, respectively.
(a) [2 marks] Compute P(M = a).
(b) [2 marks] Derive the conditional distribution of W given M = a.
Assume that, given m and w, your test score S follows a normal distribution with mean 元(m;w) := E(S|M = m;W = w) and standard deviation 5. The conditional mean function
元(m;w) is given in the table below:
The passing score is 50 or above.
(c) [3 marks] Compute the mean score E(S).
(d) [3 marks] Given that Mimi was angry, what is the mean score you would get? (e) [3 marks] Compute the probability of failing the test.
(f) [3 marks] Given that you failed the test, what is the probability that Mimi was angry?
3. [Total: 20 marks]
Note: Please append your R codes (as a separate .R file) while you submit the assignment.
Carol, an amateur economist, proposes the following time series model for unemployment
rate:
(2)
where "t ~ iid N(0; 0:022) (normal distribution with mean 0 and variance 0:022). The time period is measured in number of quarters.
(a) [3 marks] Show that the time series {yt} generated by model (1) is stationary.
(b) [3 marks] There is a stochastic cycle in the time series generated by model (1). Find its periodity in number of quarters.
(c) [4 marks] Compute the ACF for the first 3 lags, i.e., o(1), o(2) and o(3).
(d) [2 marks] Write an R program to simulate a sample path of {yt} over 30 years. Set the initial values y〇 and y━1 to be y〇 = 0:1 and y━1 = 0:12. While simulating the random numbers for "t, set the random seed to be your last 3 digits of your student ID.
(e) [2 marks] Plot the sample ACF and record its value for the Örst 3 lags (the values can be retrieved from the acf command output stored as a list). Why are they di§erent from your answers in part (c)?
(f) [3 marks] Using the simulated sample path in part (d), estimate an AR(2) model using the R command arima. Write down the estimated model with the parameter estimates and their standard error. Also record the estimated variance of the innovations. [Important note: the ìinterceptîestimate in the arima output is in fact the unconditional mean; see Rob Hyndmanís page for details: https://robjhyndman.com/hyndsight/ arimaconstants/.]
(g) [3 marks] Using the simulated sample path in part (d) and the R package forecast, plot the point forecast and the conÖdence interval for each period over the next 5 years. Describe the short-run and long-run behaviour of the point forecast and the confidence interval.
2023-03-11