RE: st: Problem with sfcross - r(3200) error

[Reut Levi <rlevi2@student.gsu.edu>]

Dear Federico,

First of all thank you for your comments. I was not aware that I need to explain where user written programs come from, but will definitely explain it in the future.  So, for any future commenters, as was already specified, the command, sfcorss, comes from the SSC.

Second, I’ve read about the rescale and restart options for the starting values, but I’m not sure I understand the reasoning behind it to determine whether I need it or not.  Nonetheless, I tried to add it to my code and I am not getting that error anymore (r 3200 – initial values not feasible).  However, it seems that convergence is not achieved because the outputs for Usigma, sigma_u and lambda are missing.  So when I try to predict my efficiency scores, using the syntax:
predict double ine, u
gen eff=exp(-ine)
I get a single efficiency score for my entire data.

As to the other suggestion you made, I don’t have previous constrained regression so I don’t think I can do that.  I’m not an expert in Stata, so if you don’t think I understood you suggestion, please clarity.

Third, as to you comment about not being able to understand if my translog cost frontier is correctly specified, can you please tell me what information should I give you so that you will able to determine that? Not every day I get to read suggestions from the actual person who wrote the command so I don’t want to pass on this opportunity!
I read the research paper series “Stochastic frontier analysis using Stata” that was written by you, but unfortunately, I was not able to follow some of the math. Also, this is the first time I’m using Stata for a research paper so, if you can, please try to simplify your response.

Thank you very much!
I appreciate your time and input,
Reut
____________________________________
From: owner-statalist@hsphsun2.harvard.edu <owner-statalist@hsphsun2.harvard.edu> on behalf of Federico Belotti <f.belotti@gmail.com>
Sent: Monday, September 30, 2013 5:05 AM
To: statalist@hsphsun2.harvard.edu
Subject: Re: st: Problem with sfcross - r(3200) error

Reut Levi <rlevi2@student.gsu.edu> have a starting values issue with the user-written command -sfcross-:

-sfcross- is from SSC and it is not an official Stata command. As Statalist FAQ clearly report,
please always explain _where_ user-written programs you refer to come from.
"This helps (often crucially) in explaining your precise problem, and it alerts readers to
commands that may be interesting or useful to them."

> I have 10 groups of data, according to percentiles of asset size.
> The command works for 3 out of my 10 groups.  However, for 7 of the groups, I’m getting the following error: r(3200) - “initial values not feasible”.  If there is a conformability error, why does the command work for 3 groups?


I cannot understand from what Levi wrote if his translog cost frontier is correctly specified. Nevertheless, it seems to me that the -moptimize- conformability error is a consequence of the "initial values not feasible" issue.
My suggestions to Levi are:

1) Read carefully the  "starting values" section in the -sfcross- help file. A solution to his problem might be the use of options -restart- and -rescale-, i.e.

sfcross lntc lnp1-lnloanslndd, distribution(hnormal) cost constraints (1 2 3) restart rescale

2) Try using starting values from a previous constrained regression, something like

cnsreg lntc lnp1-lnloanslndd, constraints(1 2 3)
mat b0 = e(b)
sfcross lntc lnp1-lnloanslndd, distribution(hnormal) cost constraints(1 2 3) svfrontier(b0)

Hope this helps,
Federico



On Sep 30, 2013, at 2:44 AM, Reut Levi wrote:

> Dear Statalist members,
>
> I am using the sfcross command to estimate inefficiency levels for the U.S. banking industry.
>
> My syntax is: sfcross lntc lnp1-lnloanslndd, distribution(hnormal) cost constraints (1 2 3)
>
> Where lntc is the natural log of total cost and lnp1-lnloanslndd are the natural logs for all of my input prices (3 types of input prices), outputs (2), and interaction terms.
> Also, my constraints syntax is as follows:
>
> constraint 1 [lnp1+lnp2+lnp3]=1
> constraint 2 [lnp1lnp1+lnp1lnp2+lnp1lnp3+lnp2lnp2+lnp2lnp3+lnp3lnp3]=0
> constraint 3 [lnp1lnloans+lnp1lndd+lnp2lnloans+lnp2lndd+lnp3lnloans+lnp3lndd]=0
>
> Where, constraint 1 is for restricting the coefficients of input prices to 1.  Constraint 2 is for restricting the coefficients of price-price interaction terms to 0. And constraint 3 is for restricting the coefficients of price-output interaction terms to 0.
>
> I have 10 groups of data, according to percentiles of asset size.
> The command works for 3 out of my 10 groups.  However, for 7 of the groups, I’m getting the following error: r(3200) - “initial values not feasible”.  If there is a conformability error, why does the command work for 3 groups?
>
> I tried a variety of things, including smaller groups, or smaller ranges for the variables; I also tried dropping all the data points for which input price or total outputs equal zero, but nothing seems to work.
>
> Please let me know if you have any other suggestions or if you can explain the problem behind this error.
> I would be happy to provide additional information about my data or my code, if needed.
> Thank you very much for your help. Have a great week,
> Reut
>
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--
Federico Belotti, PhD
Research Fellow
Centre for Economics and International Studies
University of Rome Tor Vergata
tel/fax: +39 06 7259 5627
e-mail: federico.belotti@uniroma2.it
web: http://www.econometrics.it


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