Gov2001 March 2008

gov2001@lists.gking.harvard.edu

36 participants
58 discussions

[gov2001-l] Checking results in Part (b)

by acolin＠fas.harvard.edu

Hi all, Part (b) of the problem set asks to "use Zelig to check our results." Does "results" refer only to the vector of parameter estimates or should we also check standard errors? If the latter is true, then where does Zelig store the standard errors? (Sorry for not being able to find the answer in the docs.) Thank you! -Alexei

16 years, 1 month

[gov2001-l] Someone in your class lose keys? (fwd)

by king＠harvard.edu

if anyone left their keys in class, they're with Sebastion in the IQSS main office on the 3rd floor of CGIS. Gary

16 years, 1 month

[gov2001-l] Likelihood ratio test

by vrios＠fas.harvard.edu

Hi all, Does anybody knows the mechanics and R command for applying a Likelihood-ratio test? I found this at wikipedia http://en.wikipedia.org/wiki/Likelihood-ratio_test, but I do not have a clue on what command I should use at R. Any ideas? Best, Viridiana R?os 617-997-2471

16 years, 1 month

[gov2001-l] implementing log-like function

by jbischof＠fas.harvard.edu

Hi all, I'm having trouble figuring out how a log-like function maximizing over multiple parameters would work. It seems for the "par" we would have to feed the function vectors of guesses for each of the three betas in the X matrix. How do we choose what to feed into this thing? It seems difficult to come up with guesses a priori (and unlike a probability they don't have an obvious range like [0,1]) Thanks, -- Jon Bischof Graduate Student Department of Government Harvard University

16 years, 1 month

[gov2001-l] Expected and predicted values

by jmlarson＠fas.harvard.edu

Hi all, I've uploaded a brief but more thorough explanation of expected and predicted values to the section folder on the course website. I composed the comments in an R file thinking you may find it helpful to copy and paste it into your script or into the section script. There are a couple of ways to think about predicted values, and part of the goal of the problem set is to get you thinking about that. If in doubt, explain what you did and why you think it makes sense. Happy St. Patrick's Day Eve, Jenn

16 years, 1 month

[gov2001-l] problems with logit log likelihood

by keith.schnakenberg＠gmail.com

I'm having problems implementing the log likelihood function. I used the following code: loglogit <- function(par, X=X, y=y){ beta <- par[1:ncol(X)] a <- (X*beta) b <- (1 - (2*y)) c <- 1 + exp(b%*%a) d <- log(c) out <- sum(d) } And when I give it to optim I get very unlikely coefficients and a Hessian of all zeros. I can't seem to figure out what I am overlooking. Does anybody see any obvious problems with this function? If so, I would appreciate a nudge in the right direction. Thanks, Keith

16 years, 1 month

[gov2001-l] simulations

by jmlarson＠fas.harvard.edu

Hi all, I gather there is some confusion brewing about simulating expected and predicted values. Tonight I will add more comments to the section code and re-post it to try to assist. Just remember- thinking about these sorts of things is character-building. Jenn

16 years, 1 month

[gov2001-l] Fwd: Probability - values

by jmlarson＠fas.harvard.edu

Hi Viridiana, The terms 'expected' and 'predicted' as presented on the lecture slides refer to the value of the outcome variable y, so we are interested in the difference between expected values and predicted values. In this case, an expected value is a probability, so we can use the terms expected probability and expected value interchangeably. Notice that if we average over a lot of outcome variables, we're averaging a lot of 1's and 0's, which means we're dividing the total number of 1's by the total number of 1's and 0's, which means we get a probability of o-ring failure. (hence, the last step in simulating an expected value returns a probability). You rightly point out that the dependent variable in this case is dichotomous- either o-rings fail or they do not; y can only be a zero or a one. To estimate one expected value, you draw one set of betas (a B0 and a B1), fix your x's, and calculate a probability using the function you mentioned (1/(1+e^(-Bxi)) ). That function will return n probabilities, where n is the number of observations. Plug those n probabilities in to the stochastic component to get n y's, average those n y's, and you have one expected value/expected probability. (note that these last two steps are superfluous in the case of a logit model). Hope this helps, Jenn On Sat, Mar 15, 2008 at 3:33 PM, Viridiana Rios <vrios at fas.harvard.edu> wrote: > Hi all, > > Can anybody please, explain to me the difference between expected values > and expected probability in the context of a dichotomic dependent variable? > > Here is my confusion: We have a probit model (y=B0+B1x1). We draw 1000 > Betas from a normal distribution. We calculate y=B0+B1x1 using all the Betas > of the draw. So, now we have 1000 different values of y (one for each draw > of Betas). Then, we transform y to a probability using the function > 1/(1+e^(-Bxi)). Now we have 1000 different probabilites. Are these > probabilities the expected probability or the expected value? If these are > the expected probabilities, howe can I get the expected values? Are the > expected values the 1000 values of y? > > Best, > > Viridiana R?os > 617-997-2471 >

16 years, 1 month

[gov2001-l] Probability - values

by vrios＠fas.harvard.edu

Hi all, Can anybody please, explain to me the difference between expected values and expected probability in the context of a dichotomic dependent variable? Here is my confusion: We have a probit model (y=B0+B1x1). We draw 1000 Betas from a normal distribution. We calculate y=B0+B1x1 using all the Betas of the draw. So, now we have 1000 different values of y (one for each draw of Betas). Then, we transform y to a probability using the function 1/(1+e^(-Bxi)). Now we have 1000 different probabilites. Are these probabilities the expected probability or the expected value? If these are the expected probabilities, howe can I get the expected values? Are the expected values the 1000 values of y? Best, Viridiana R?os 617-997-2471

16 years, 1 month

[gov2001-l] [POLMETH] REMINDER: PolMeth XXV: Applications Due in ONE Week!!!! (fwd)

by king＠harvard.edu

---------- Forwarded message ---------- Date: Fri, 14 Mar 2008 11:58:09 -0400 From: "Franzese, Robert" <franzese at UMICH.EDU> Reply-To: Political Methodology Society <POLMETH at ARTSCI.WUSTL.EDU> To: POLMETH at ARTSCI.WUSTL.EDU Subject: [POLMETH] REMINDER: PolMeth XXV: Applications Due in ONE Week!!!! Hi Folks, Just another pestering reminder about PolMeth XXV: The deadline for applications to the conference is now in 1 week!!! 20 March 2008 To apply to attend the meetings, complete the application form at the Society's webpage by 20 March 2008: http://polmeth.wustl.edu/conferences/methods2008/register/ Submit a paper proposal, a poster proposal, a proposal to attend, and/or a proposal indicating your willingness to serve as discussant. Further Reminders: We have expanded the planned size of the conference, so there will be plenty of space for a much higher percentage of applicants to attend and, if the supply of proposals suffices, of poster/paper proposals to be accepted. Faculty may propose to present in poster or paper sessions and, if they propose papers, may be assigned nonetheless to a poster-presentation at the conference-organizers sole discretion. (Almost assuredly, if you propose a poster, you will get that format if accepted.) Graduate students are urged to propose a poster for the graduate-student poster-session, and those who do will receive higher priority for the limited funding we have, but students may also propose simply to attend. So: APPLY! DEADLINE: 20 March 2008 Apologies for the clutter &/or cross-postings. Looking forward to seeing you there! Rob P.S. Did I mention? DEADLINE: 20 March 2008 The original call follows: -----Original Message----- From: franzese at umich.edu [mailto:franzese at umich.edu] Sent: Tuesday, February 19, 2008 8:39 AM To: Franzese, Robert Subject: PolMeth XXV: Call for Applications to Participate CALL FOR PROPOSALS: PolMeth XXV: The 25th Annual, Silver Edition Summer Meeting of the Society for Political Methodology The University of Michigan, Ann Arbor 9 - 13 July 2008 (Core Program: 10-12 July 2008) The 25th Annual, Silver Edition, Summer Methodology Conference will be held 10-12 July 2008, on the campus of the University of Michigan, Ann Arbor. Sponsors of these meetings are the Institute for Social Research of the University of Michigan, the National Science Foundation, and the Society for Political Methodology. To apply to attend the meetings, complete the application form at the Society's webpage by 20 March 2008: http://polmeth.wustl.edu/conferences/methods2008/register/ DEADLINE FOR APPLICATIONS: 20 March 2008. All applicants will propose to present a poster or a paper, and/or to act as a discussant, or simply to attend. Although graduate students may also apply simply to attend, they are strongly encouraged to propose a poster for the graduate-student poster-session, which is a venerated tradition and outstanding professional opportunity offered by the conference. Graduate students (and other eligible applicants) proposing and having accepted a poster (or a paper) will receive priority consideration for funding if they apply for it (see below). To accommodate the continued growth of the conference in response to great and strongly rising demand--we expect a further approximately 50% increase in size from last year's expanded total of about 160 attendees--we have made a number of small adjustments in the format of the conference, requiring corresponding alterations of the application and registration processes. SUMMARY OF THE REVISED PROGRAM-FORMAT (much further information available at the conference web-site: http://polmeth.wustl.edu/conferences/methods2008/): The conference program will consist of: One day (Thursday, 10 July) of plenary sessions (i.e., sessions of the whole) of paper presentations, with discussant & open discussion. One day (Friday, 11 July) of split-sessions, split in two or possibly three, of paper presentations with discussant & open discussion or of poster session(s), but not both types simultaneously. One day (Saturday, 12 July) of split-sessions, split in two, of paper presentations with discussant & open discussion or of poster session(s), but not both types simultaneously. Also planned for Thursday: the traditional keynote lecture by a prominent, non-political-science, methodologist from U of M, and our business meeting, followed by a opening-evening reception. Also planned for Friday: the traditional graduate-student poster-session, accompanied by an evening reception. Also planned for Saturday: a closing dinner-reception. A new tradition: NSF has funded also a dinner, reception, and/or other event for Women in Political Methodology, tentatively scheduled for Wednesday evening. (This will be the third such event.) An even newer tradition: An add-on mini-conference/workshop or two may be held Wednesday PM and/or Sunday AM, on topics and of a format TBA. Announcements as those develop will go to this email list and the conference web site. The core conference begins Thursday morning and ends Saturday evening, so attendees should plan to arrive Wednesday the 9th and depart Sunday the 13th. To accommodate the expanded size, we have increased the numbers of split sessions, and, also partly in response to that increased size, we intend to expand usage of the poster-session format. Poster presentations and split-session paper-presentations will be scheduled and treated as full equals in every regard with plenary paper-presentation sessions. Applicants may propose a poster or a paper, but the program committee will assign accepted paper-proposals to plenary-sessions, to split-session paper-presentations, or to poster-session presentations entirely on their own discretionary judgment regarding optimal conference design, balance, and flow. NOTABLE REGARDING THE REVISED APPLICATION & REGISTRATION PROCESSES: Following acceptance and upon registration, all conference attendees will pay or have paid for them the $200 conference registration fee. (This is the same amount as the faculty-registration fee last year, but now all attendees will pay it. This is also approximately equal to the variable cost per person of the conference.) The fee is collected in the registration process (via PayPal), and registration cannot be validly completed without payment. Newly expanded this year, the NSF will fund the attendance of 55 (total) graduate students, women, minorities, and assistant professors. (Great & sincere gratitude is hereby extended from us all to PI's Jan Box-Steffensmeier & Phil Schrodt.) The acceptance committee will review applications for funding (which, procedurally, amount to the applicant indicating her/his wish to be considered for funding and then checking boxes for the categories by which s/he is eligible), and winners of funding will be notified along with their acceptance to the conference. Also new this year, all graduate-student applicants will be required to give the email address not only of a faculty recommender, which has long been required, but also to give the email address of a "guarantor of funding." The guarantor may be the same faculty member as the recommender, a different faculty member, someone authorized to commit an institutional source of funding, or even the graduate student her/himself. The guarantor commits to paying or having paid the registration fee for the graduate student in the case that student does not win funding. The option of the student listing her/himself as guarantor allows students wishing (or able and willing and needing) to pay their own registration to do so. The options, purposefully listed first, of naming a faculty or institutional guarantor are intended to emphasize heavily the strong and good norm that faculty/departmental/institutional sponsors should pay for their students to attend the conference. ANNOUNCEMENT OF ACCEPTANCES & OF FUNDING SHOULD ARRIVE AROUND MID-APRIL. Following that, LODGING _MUST_ BE BOOKED/CONFIRMED BY END OF MAY. Technical questions regarding the application & registration web-site should be directed to Stephen Haptonstahl (srhapton at wustl.edu). Substantive questions or comments regarding the application process, the conference, or the conference web-site should be directed to Rob Franzese (franzese at umich.edu) or the graduate-student assistant for the conference & conference web-site, Bryce Corrigan (becorrig at umich.edu). We look forward to seeing you in Ann Arbor this summer! ************************************************************************ * Robert (Rob) J. Franzese, Jr. US Mail: (Room 4246 ISR) Associate Professor, P.O. Box 1248 Department of Political Science, Ann Arbor, MI 48106-1248 and Research Associate Professor, (Currier: 426 Thompson St.) Center for Political Studies, e-mail: franzese at umich.edu Institute for Social Research, office: 1-734-936-1850 The University of Michigan fax: 1-734-764-3341 http://www-personal.umich.edu/~franzese ************************************************************************ * ********************************************************** Political Methodology E-Mail List Editors: Melanie Goodrich, <melaniegoodrich at nyu.edu> Delia Bailey, <dbailey at wustl.edu> ********************************************************** Send messages to polmeth at artsci.wustl.edu To join the list, cancel your subscription, or modify your subscription settings visit: http://polmeth.wustl.edu/polmeth.php ********************************************************** ********************************************************** Political Methodology E-Mail List Editors: Melanie Goodrich, <melaniegoodrich at nyu.edu> Delia Bailey, <dbailey at wustl.edu> ********************************************************** Send messages to polmeth at artsci.wustl.edu To join the list, cancel your subscription, or modify your subscription settings visit: http://polmeth.wustl.edu/polmeth.php **********************************************************

16 years, 1 month

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Gov2001 March 2008