MGSC 291 Exam 3 Prep
make date variable be recognized as a date in R with the as.Date() function - ANS-What is the
first step in processing you data for a time series analysis in R?
- make all data factors
- make date variable a factor with the factor() function
-make date variable be recognized as a date in R with the as.Date() function
as the number of days relative to Jan 1, 1970 - ANS-How does R store date variables?
-as factors
-as characters
-as the number of days relative to Jan 1, 1970
seasonal variation - ANS-In a time series, regular variation that is repeated within a year is
called....
-non-stationary
-seasonal variation
-a random walk
diverging series - ANS-Which of the following types of series are useless for modeling?
- random walk
- diverging series
- mean reverting, stationary
stationary, mean reverting - ANS-Which of the following is the most useful type of series for
modeling?
- random walk
- diverging series
- stationary, mean reverting
- ANS-Match the coefficient on the AR(1) term in a regression to the correct series
random walk - ANS-|beta| = 1
- random walk
- mean reverting
-diverging
mean reverting - ANS-|beta| < 1
- random walk
- mean-reverting
-diverging
, diverging - ANS-|beta| > 1
- random walk
- mean reverting
-diverging
use the returns transformation for modeling - ANS-if you have a random walk, what should you
do?
-use the returns transformation for modeling
- incorporate other important trend variables
- scrap the data - this type is useless
- the simple interrelations of the AR(1) term no longer apply
- if you need higher lags, you might have missed an important trend or seasonality -
ANS-(WHICH 2 APPLY) What is true about adding higher than AR(1) lags to a model?
- the simple interrelations of the AR(1) term no longer apply
-this model always works better for prediction than the model with only the AR(1) term
-you almost always need to take a log of the response
- if you need higher lags, you might have missed an important trend or seasonality
- you might have modeled the wrong response
an inelastic good - ANS-A sales price elasticity greater than -1 implies
- an inelastic good
- a good model fit
- a random walk-
-a diverging series
panel data - ANS-When you have multiple stacks of time series, for example a time series of
monthly sales for 185 stores, you have
- a random walk
- a mean reverting time series
- panel data
- no need for fixed effects
-are different from random effects which allow for correlations between the error terms
- are just simply a way to include factor variable into the regression - ANS-(WHICH 2 APPLY)
Fixed effects are:
- effects that fix your residuals to be uncorrelated
-are different from random effects which allow for correlations between the error terms
-are just simply a way to include factor variables into the regression
-make it unnecessary to check model fit since they fix errors in the regression
underestimate of uncertainty - ANS-Dependencies in the data often lead to an
-underestimate of uncertainty
-an overestimate of uncertainty
The benefits of buying summaries with Stuvia:
Guaranteed quality through customer reviews
Stuvia customers have reviewed more than 700,000 summaries. This how you know that you are buying the best documents.
Quick and easy check-out
You can quickly pay through credit card or Stuvia-credit for the summaries. There is no membership needed.
Focus on what matters
Your fellow students write the study notes themselves, which is why the documents are always reliable and up-to-date. This ensures you quickly get to the core!
Frequently asked questions
What do I get when I buy this document?
You get a PDF, available immediately after your purchase. The purchased document is accessible anytime, anywhere and indefinitely through your profile.
Satisfaction guarantee: how does it work?
Our satisfaction guarantee ensures that you always find a study document that suits you well. You fill out a form, and our customer service team takes care of the rest.
Who am I buying these notes from?
Stuvia is a marketplace, so you are not buying this document from us, but from seller topgradesdr. Stuvia facilitates payment to the seller.
Will I be stuck with a subscription?
No, you only buy these notes for $7.99. You're not tied to anything after your purchase.