Tag: ARIMA

New Free Online Book by Rob Hyndman on Forecasting using #Rstats

From the creator of some of the most widely used packages for time series in the R programming language comes a brand new book, and its online!

This time the book is free, will be updated and 7 chapters are ready (to read!)

. If you do forecasting professionally, now is the time to suggest your own use cases to be featured as the book gets ready by end- 2012. The book is intended as a replace­ment for Makri­dakis, Wheel­wright and Hyn­d­man (Wiley 1998).

http://otexts.com/fpp/

The book is writ­ten for three audi­ences:

(1) people find­ing them­selves doing fore­cast­ing in busi­ness when they may not have had any for­mal train­ing in the area;

(2) undergraduate stu­dents study­ing busi­ness;

(3) MBA stu­dents doing a fore­cast­ing elec­tive.

The book is dif­fer­ent from other fore­cast­ing text­books in sev­eral ways.

  • It is free and online, mak­ing it acces­si­ble to a wide audience.
  • It is con­tin­u­ously updated. You don’t have to wait until the next edi­tion for errors to be removed or new meth­ods to be dis­cussed. We will update the book frequently.
  • There are dozens of real data exam­ples taken from our own con­sult­ing prac­tice. We have worked with hun­dreds of busi­nesses and orga­ni­za­tions help­ing them with fore­cast­ing issues, and this expe­ri­ence has con­tributed directly to many of the exam­ples given here, as well as guid­ing our gen­eral phi­los­o­phy of forecasting.
  • We empha­sise graph­i­cal meth­ods more than most fore­cast­ers. We use graphs to explore the data, analyse the valid­ity of the mod­els fit­ted and present the fore­cast­ing results.

A print ver­sion and a down­load­able e-version of the book will be avail­able to pur­chase on Ama­zon, but not until a few more chap­ters are written.

Contents

(Ajay-Support the open textbook movement!)

If you’ve found this book helpful, please consider helping to fund free, open and online textbooks. (Donations via PayPal.)

Look for yourself at http://otexts.com/fpp/

 

FaceBook IPO- Who hacked whom?

Some thoughts on the FB IPO-

1) Is Zuck reading emails on his honeymoon? Where is he?

2) In 3 days FB lost 34 billion USD in market valuation. Thats enough to buy AOL,Yahoo, LinkedIn and Twitter (combined)

3) People are now shorting FB based on 3-4 days of trading performance. Maybe they know more ARIMA !

4) Who made money on the over-pricing in terms on employees who sold on 1 st day, financial bankers who did the same?

5) Who lost money on the first three days due to Nasdaq’s problems?

6) What is the exact technical problem that Nasdaq had?

7) The much deplored FaceBook Price/Earnings ratio (99) is still comparable to AOL’s (85) and much less than LI (620!). see http://www.google.com/finance?cid=296878244325128

8) Maybe FB can stop copying Google’s ad model (which Google invented) and go back to the drawing table. Like a FB kind of Paypal

9) There are more experts on the blogosphere than experts in Wall Street.

10) No blogger is willing to admit that they erred in the optimism on the great white IPO hope.

I did. Mea culpa. I thought FB is a good stock. I would buy it still- but the rupee tanked by 10% since past 1 week against the dollar.

 

I am now waiting for Chinese social network market to open with IPO’s. Thats walled gardens within walled gardens of Jade and Bamboo.

Related- Art Work of Another 100 billion dollar company (2006)

Using R for Time Series in SAS

 

Time series: random data plus trend, with best...
Image via Wikipedia

 

Here is a great paper on using Time Series in R, and it specifically allows you to use just R output in Base SAS.

SAS Code

/* three methods: */

/* 1. Call R directly – Some errors are not reported to log */

x “’C:\Program Files\R\R-2.12.0\bin\r.exe’–no-save –no-restore <“”&rsourcepath\tsdiag.r””>””&rsourcepath\tsdiag.out”””;

/* include the R log in the SAS log */7data _null_;

infile “&rsourcepath\tsdiag.out”;

file log;

input;

put ’R LOG: ’ _infile_;

run;

/* include the image in the sas output.Specify a file if you are not using autogenerated html output */

ods html;

data _null_;

file print;

put “<IMG SRC=’” “&rsourcepath\plot.png” “’ border=’0’>”;

put “<IMG SRC=’” “&rsourcepath\acf.png” “’ border=’0’>”;

put “<IMG SRC=’” “&rsourcepath\pacf.png” “’ border=’0’>”;

put “<IMG SRC=’” “&rsourcepath\spect.png” “’ border=’0’>”;

put “<IMG SRC=’” “&rsourcepath\fcst.png” “’ border=’0’>”;

run;

ods html close;

The R code to create a time series plot is quite elegant though-


library(tseries)

air <- AirPassengers #Datasetname

ts.plot(air)

acf(air)

pacf(air)

plot(decompose(air))

air.fit <- arima(air,order=c(0,1,1), seasonal=list(order=c(0,1,1), period=12) #The ARIMA Model Based on PACF and ACF Graphs

tsdiag(air.fit)

library(forecast)

air.forecast <- forecast(air.fit)

plot.forecast(air.forecast)

You can download the fascinating paper from the Analytics NCSU Website http://analytics.ncsu.edu/sesug/2008/ST-146.pdf

About the Author-

Sam Croker has a MS in Statistics from the University of South Carolina and has over ten years of experience in analytics.   His research interests are in time series analysis and forecasting with focus on stream-flow analysis.  He is currently using SAS, R and other analytical tools for fraud and abuse detection in Medicare and Medicaid data. He also has experience in analyzing, modeling and forecasting in the finance, marketing, hospitality, retail and pharmaceutical industries.

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Predictive Forecasting in Commercial Applications

Most organizations tend to have a sales plan or forecast for the next 1 year.This is done for internal planning as well as give guidance to financial investment analysts covering the listed company.

However a lot of organizations use simplistic linear models of

1) either growth based on previous history (Last year Sales * Factor of forecast (e.g 10 % growth in sales) -TIME SERIES APPROACH

OR

2) growth based on macro economic causal factors (e.g economy is in recession hence sales will grow by 3 %) REGRESSION BASED APPROACH and

3) A consensus of industrial factors (We have spare capacity of 10 % so we will likely slash prices and have sales growth of 2 % but profit growth of -3%) DELPHI BASED APPROACH (this is also based on bottoms up market feedback and top down sales pressure).

A better approach is to combine all these approaches in one or different models .

This can help build a much more robust forecasting model for organizations using nothing more than simple combination of excel cells.

The following model assumes only seven factors and tries to build a stable and relatively easy to understand forecast model.

Forecasted Sales for this quarter =

Historic Sales for this quarter last year *A1

+ Historic Average Sales for this quarter for past three -five years (based on industry cycle ups -downs)*A2

+ Historic Sales for this quarter/Actual Sales of Last Quarter( for seasonal factors )*A3

+Causal Factor 1 ( Eg. Outsourcing is likely to grow by 15 % in this year) *A4

+Causal Factor 2 (Foreign Exchange Movement.Dollar is likely to depreciate by 10 %)*A5

+ Causal Factor 3 (Our bench strength is likely to grow by 3 % in this quarter)*A6

+ Percentage Error Factor *A7 (There will always be +-5 to15 % error in forecasts.Capturing this error also helps provide a feedback loop for planning).

Here A1- A7 are constants

In order to get actual values of A1-A7 , run this a regression (use the add-in and tools menu in excel) on actual data for past three years quarters (keeping last six months seperate)

Then run the actual equation on last two quarters and check for actual error. If error exceeds the comfort level (+-3 % for critical industries and +-15 % for harder to predict industries) . Iterate the last two steps till you get a good equation.

Then substitute in the 7 factor predictive model to build your simple and robust sales plan for this quarter.

Happy forecasting !!!

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