Recall the moving average model dt = et − θet−1, where et are
independent with mean...
Recall the moving average model dt = et − θet−1, where et are
independent with mean 0 and variance σ2. Find its autocorrelation
function ρk = Cor(dt,dt−k).
Consider the model Yt = ΦYt−3 + et − θet−1, where et has
variance σ 2 .
(a) Identify Yt as a certain SARIMA(p, d, q) × (P, D, Q)s model.
That is, specify each of p, d, q, P, D, Q, and s. You may assume
that Φ < 1.
(b) Find the variance of Yt .
(c) What are the forecasts for Yt+1 and Yt+4?
(d) What are the error variances for your forecasts above?
(e) If σ...
1. Evaluate the forecasting model using 3 month moving
average, and 3 month moving weighted average, and exponential. The
weights are .5 for the most recent demand, .25 for the other
months. Alpha = .3. Use the weighted moving average for January
Forecast.
Actual Demand
Oct
300
Nov
360
Dec
425
Jan
405
Feb
430
March
505
April
550
May
490
2. Calculate MAD and MAPE for each and compare. Which
method is a better forecast and why?
5. The population of certain small organism grows according to
the model: dy/dt = 5y where y=20 when t=0
t is measured in months. a) Construct the specific function for
y. b) Find how many in the population of this organism after 8
months. c) Determine how many months until there are 228 of this
organism. Round to the nearest 0.1
What are the differences between autoregressive and moving
average models? Consider the following: model specifications,
stationarity, the shapes of their autocorrelation and partial
autocorrelation functions.
Consider the model as yt= βyt-1
+et, which describes the dynamics of price of a
company’s stock (y).
a. Assuming that et has zero mean, constant variance
σe2 and is not serially correlated, obtain
expressions for E(yt), var(yt) and
cov(yt, yt-1 ) and the first-order auto
correlation coefficient. Does y represent a stationary process?
Explain briefly.
b. If now et follows an AR(1) process, that is
et =ρet-1 +vt, where vt
is white noise and 0 < ρ < 1,...
Let X1, …
, Xn be independent where Xi is normally
distributed with unknown mean µ and unknown variance o2 > 0.
Find the likelihood ratio test for testing that µ = 0
against
−∞ < µ < ∞.
Let X1, … , Xn be independent where
Xi is normally distributed with unknown mean µ and
unknown variance o2 > 0.
Find the likelihood ratio test for testing that µ = 0
against
−∞ < µ < ∞.
Question 1 contains the actual values for 12 periods (listed in
order, 1-12). In Excel, create forecasts for periods 6-13 using
each of the following methods: 5 period simple moving average; 4
period weighted moving average (0.63, 0.26, 0.08, 0.03);
exponential smoothing (alpha = 0.23 and the forecast for period 5 =
53); linear regression with the equation based on all 12 periods;
and quadratic regression with the equation based on all 12 periods.
Round all numerical answers to two...