Amelia December 2002

amelia@lists.gking.harvard.edu

6 participants
9 discussions

by Gary King

On Fri, 20 Dec 2002, Kevin Timothy Arceneaux wrote: > Prof. King, > > My understanding is that interactions, which will be used in the analysis, > should be included in the imputation data set. Say I have missing values > in X1 and X2, which produce missing values in X1*X2. Amelia will impute > values for X1, X2, and X1*X2, but it will not necessarily be the case that > the imputed values for X1*X2 will equal the multiplication of X1 and X2. > Is there a way to set this sort of constraint in Amelia? (I am using the > Windows version). > > If not, would it be appropriate to set the missing values in X1*X2 to some > arbitrary number (e.g., -9) and then recomputed the interaction with the > imputed values for each of the resulting imputed data sets? Or should I > allow Amelia to impute missing values in X1*X2, and then correct these > values in the resulting imputed data sets? Good question. I would alow Amelia to impute x1*x2 and then recompute them from the contituent (imputed) variables. that allows the interaction to have an effect and it produces consistent estimates. One issue in Amelia (and all methods of imputation) is that if x1 is missing for a variable but x2 is observed, x1*x2 will be coded as missing even though it is partially observed. nothing you can do about this tho. Gary : Gary King, King(a)Harvard.Edu http://GKing.Harvard.Edu : : Center for Basic Research Direct (617) 495-2027 : : in the Social Sciences Assistant (617) 495-9271 : : 34 Kirkland Street, Rm. 2 HU-MIT DC (617) 495-4734 : : Harvard U, Cambridge, MA 02138 eFax (928) 832-7022 : > > Thanks for your help, > Kevin. > > > Kevin Arceneaux > Ph.D. Candidate > Department of Political Science > Rice University > 6100 Main St., MS 24 > Houston, TX 77005 > (713) 348-2107 >

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21 years, 4 months

RE:Time series option

by Akunda, Eric

I am trying to use the time series option in the windows version of Amelia (I was able to read in the data successfully as text after the initial problems). How do I specify the interperiod length (in the manual, it is stated that you type 1 if your data are yearly) when my data are monthly in defining the AMtstep? Thanks for your help. Eric Akunda.

21 years, 4 months

RE:AMELIA-reading data files.

by Akunda, Eric

I am trying to read a data set into Amelia (I am a first time user!) but failing. My computer runs Windows 2000 Professional. I have saved the data as a Microsoft Excel 2.1 file named ssri.xls. The data set has 20 variables with a total of 498 observations that are a pooled data set of five different products. When I try to input the file I type C:\ssri.xls which resides in the C:\ drive noting the initial problems I had experienced with even trying to run Amelia itself from folders with longer names (at least I ran the example with sample.asc and it worked!). When I type enter, I get a message that reads as follows: C:\DOCUM~1\Eric\LOCALS~1\Temp\dload$$$.fmt' exit status 3 Error: Program was unable to read file contents. Please check instructions to make sure input is of correct type. I know this may have happened to someone else but having gone through the threads in the archives of the listserv, I was not able to see this addressed (and did not find it in the FAQs). Is it a problem that's unique to me? Thanks for your time and answering the query. Eric. Eric A. Akunda Doctoral Student (Marketing) Kenan-Flagler Business School University of North Carolina - Chapel Hill CB # 3490 McColl Chapel Hill, NC 27599-3490 Tel: 919-962-0783 Voice: 919-918-1222 Fax: 919-962-7186 Email: eric_akunda(a)unc.edu <mailto:eric_akunda@unc.edu>

21 years, 4 months

Re: Amelia question

by Gary King

On Sat, 7 Dec 2002, Diogo L Pinheiro wrote: > Dear Dr. King, I have a 55x17 TSCS data set with about 40 variables. The > model I intend to run afterwards involves using dummy variables for > countries and time. When I use Amelia with all these dummies, the > program will disappear a few seconds after I hit run (i get the screen > Amelia Begins, and then it all disapears). I've tried including the > dummies both manually and by setting amusecs=1 and amusets=1 and setting > it as a nominal variable. I've got a AMD 1.2 Ghz computer with 256 mb of > RAM. Is ther anything I can do? (I've set the max_workspace do different > values, from 100 do 200, and I always get the same.) if you're using the features for TSCS variables, then you may have an enormous number of variables. the number of parmaters in Amelia goes up fast in the number of variables, and so this may be the problem. I suggest (in addition to counting exactly how many variables you are implicitly using) you try it with a small number of variables, get that to work, and then gradually increase. > Also, another problem that I often run into is that sometimes I will set > Amfully correctly, and when I start to run Amelia, I get a message > saying that Amfully is not properly defined. After I get that message I > go back to the AMfully screen and for some reason the values there are > different from the ones I entered. I found that that happens to most > fields after getting the error message, and so I have to reset all the > values. Are there any solutions for that? By the way, I use the windows > version. Thanks Diogo Pinheiro > Amelia for windows works by checking all the global values and resetting any that are invalid. So that's a feature, or at least it was by design, and not really a bug. Tho I see your point.. Gary : Gary King, King(a)Harvard.Edu http://GKing.Harvard.Edu : : Center for Basic Research Direct (617) 495-2027 : : in the Social Sciences Assistant (617) 495-9271 : : 34 Kirkland Street, Rm. 2 HU-MIT DC (617) 495-4734 : : Harvard U, Cambridge, MA 02138 eFax (928) 832-7022 :

21 years, 4 months

RE:AMELIA

by Gary King

I'd take the square root or log-plus-one to transform your data to a more normal scale before Amelia and then untransform after. otherwise, the time-series-cross-sectional aspect will be the most difficult. I would use Amelia's special features for these types of data, but then you should carefully check the imputations, as it seems you have been doing, to make sure they're reasonable. Amelia should work in these situations a good deal better than SAS because of these features, but it will not necessarily fix all the problems. Best of luck with your research, Gary King : Gary King, King(a)Harvard.Edu http://GKing.Harvard.Edu : : Center for Basic Research Direct (617) 495-2027 : : in the Social Sciences Assistant (617) 495-9271 : : 34 Kirkland Street, Rm. 2 HU-MIT DC (617) 495-4734 : : Harvard U, Cambridge, MA 02138 eFax (928) 832-7022 : On Mon, 2 Dec 2002, Akunda, Eric wrote: > Dear Prof King, > > I have a data set that has missing values for some variables in the > following way. I would like to describe the missing data to determine > whether using Amelia will be appropriate (I have read the article that > accompanies Amelia). > > My data are for the pharmaceutical industry. I have # of prescriptions > sold as my response (which I convert to market shares). I then have as > covariates the # of minutes the salespeople detail to physicians, the > counts of these details, the detailing expenditures (in dollars), the > price per prescription in dollars, the expenditure on direct-to-consumer > advertising, the events and meetings expenditures (in dollars), and > journal advertising. The latter three variables are incomplete because > the firm collecting the data (from whom we purchased the same) did not > collect the data at the time, and seems to have began to collect these > variables on enquiries from its clients. The data are time series > (monthly) and cross-sectional (by brand), and based on the fact that the > brands enter the market sequentially create and unbalanced panel. I > intend to use Amelia (the time-series cross-sectional function) to > impute the missing values. However, my question is, would this be > appropriate, based on the fact that the data are not really missing at > random? Would this necessitate coming up with a specification unique to > the data as you have advised in the paper? Eliminating observations in > this dataset is unthinkable because the observations are very few (about > 500 for the pooled brands including those with missing values on the > three covariates). I have tried to impute the data using proc MI in sas > (based on the book by Paul Allison), but some of the imputed values were > poor. I have the feeling that the importance resampling coupled with > specifying a range for the missing values would improve the imputations > (especially so because the specification for the panel data is clearer > compared to the proc mi specification based on "my" understanding of > both). What would your advice be? Thanks very much in advance for taking > your precious time to provide an answer. I will update you on my > experiences with using Amelia for this dataset. > > Kindest regards, > Sincerely, > Eric Akunda. > PhD student, Marketing. > University of North Carolina at Chapel Hill. >

21 years, 4 months

Re: MIEST

by Gary King

Clarify is now Amelia-ready in the sense that there are facilities within it to use multiply imputed data sets. So you don't need other software any longer. For details of how to use this, see http://gking.harvard.edu/clarify/docs/node26.html Thanks for your interest. Gary King : Gary King, King(a)Harvard.Edu http://GKing.Harvard.Edu : : Center for Basic Research Direct (617) 495-2027 : : in the Social Sciences Assistant (617) 495-9271 : : 34 Kirkland Street, Rm. 2 HU-MIT DC (617) 495-4734 : : Harvard U, Cambridge, MA 02138 eFax (928) 832-7022 : On Mon, 2 Dec 2002 TxLiberal(a)aol.com wrote: > I am in a Mulitvariate class at the University of Houston. We are using > Stata, Clarigy and Amelia and were told to use the MIEST command in > Stata. However, we cannot find where to download the MIEST software. > Any assistance you could offer would be greatly appreciated. > > Thanks, > > Tom >

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21 years, 4 months

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Amelia December 2002