Gov2001 February 2009

gov2001@lists.gking.harvard.edu

31 participants
46 discussions

[gov2001-l] R command for tabulating frequency

by rwest817＠gmail.com

Very elementary question, I'm sure, but I'm new to R : What is a command in R which would return the frequency elements in a vector, and could be applied with "any" to recognize when a threshold frequency has been achieved? For example, if I have a vector n <- [1, 2, 3, 4, 1, 2, 3, 2, 1, 2], is there a command that will output the number of instances of the most frequent element (i.e, "2" is repeated 4 times), or something similarly useful? Thanks, Rachel

15 years, 2 months

[gov2001-l] PS1 graded

by woolfalk＠fas.harvard.edu

Hi All, PS 1 is graded. For those who handed in a hard copy of the problem set: Your write up (with grade and brief comments) will be returned to you during section on Thursday. For those who submitted the problem set by email because the dropbox was unavailable to them: Your grade (with brief comments) will be emailed to you. Also, *please square away your registration as soon as possible! Check to see if you now have access to the ps dropbox. If not, contact the registrar and make sure they have the required paperwork and that everything is being processed. Getting you registered is important for a handful of reasons including signing you up for access to lecture and section videos (remember: access will be restricted to non-extension students after the shopping period is over).* For those who only submitted their problem set to the dropbox (i.e.g did not hand in a hard copy of the problem set or submit the problem set by email): Your grade (with brief comments) is posted as a "comment" under the uploaded file for your write up in the dropbox. Thanks, Miya -- Miya Woolfalk Ph.D. Student Harvard University Government and Social Policy

15 years, 2 months

[gov2001-l] Clarification on pset 2, question 2

by jpferg＠mit.edu

Hi all, The wording on questions like this always confuses me. We are asked, "If a researcher interviews 5 separate individuals [out of the 25 in the village] randomly selected with equal probability, what is the probability that she will not talk to a single supporter of the government?" I seems like you could treat this two ways: 1. What is the probability of getting 0 successes in 5 draws from a population of arbitrary size but fixed probability of success? If you did it this way, you'd use the binomial distribution with n = 5, k = 0 and pi = 6/25. 2. What is the probability of getting 5 sequential failures in 5 draws from a population of 25 where there are 6 potential "successes"? If you did it this way, you'd use the hypergeometric distribution with k = 0, N = 25, m = 6 and n = 5. The second approach feels more natural, but is it? John-Paul

15 years, 2 months

[gov2001-l] ps1 solutions

by woolfalk＠fas.harvard.edu

Hi Folks, I encourage you all to take a look at the solution set (especially the R code) before getting too far into working on ps2. Although many of you were able to successfully complete ps1, there are more efficient ways to answer many of the questions in ps1 (e.g. using apply() rather than for() ). Neat and concise code is generally always better. Miya -- Miya Woolfalk Ph.D. Student Harvard University Government and Social Policy

15 years, 2 months

[gov2001-l] Clarification to homework policy

by woolfalk＠fas.harvard.edu

Hello, *EVERYONE:* When you *submit your problem sets to the problem set drop box*, we want *two files*: (1) A *write up *of your homework in *pdf format*: This write up should contain your *answers to the problem set questions* (e.g. tables, figures, explanations, etc). It should also contain *all code necessary to complete each problem*. The relevant code should appear in the corresponding section of your write up (e.g. the code to answer question 2.1 should appear directly under your answer to question 2.1). I have updated the write up for the solutions to problem set 1. Please have a look to make sure that your write up for each future problem set follows this format. (2) A *txt or r file *with all of your *R code:* This file should contain *all of the commands necessary to answer the questions* in the problem set. It should be able to reproduce all of your answers in the problem set write up and run without errors. We recommend that you clear the workspace and re-run all of your code before submitting your problem set. This will make sure that everything runs without errors. This file *should be written using an editor* (the R editor or otherwise) and should not be produced by copying and pasting the R console into a txt file. *NON-EXTENSION STUDENTS:* When you *submit the hard copy of your problem set in section*, we want *one document*, your problem set *write up*. Thanks, Miya -- Miya Woolfalk Ph.D. Student Harvard University Government and Social Policy

15 years, 2 months

[gov2001-l] Corrections from section

by plam＠fas.harvard.edu

Hi all, Two mistakes I made on my slides for section. 1. Jensen's inequality is E(g(X)) >= g(E(X)) for convex functions only. The inequality switches signs for concave functions. 2. The coding error in my simulation problem is that I neglected to account for the fact that I took out one marble in the first urn after the first draw. When I do my final draw, the urn has one more marble in it than it should. Think about how you would correct that. -- Patrick Lam Department of Government and Institute for Quantitative Social Science, Harvard University http://www.people.fas.harvard.edu/~plam

15 years, 2 months

[gov2001-l] IMPORTANT: modification to homework policy

by woolfalk＠fas.harvard.edu

Hi Folks, Please be sure to submit your problem set writeup as a pdf document. The R code can either be in .r or .txt format. Students who already uploaded their write-up and R code but did so in a different format: Please delete the existing files and upload your homework in the correct format. I realize that this was not stated in the homework policy document and apologize for any inconvenience. We are making this change to the policy mainly because older versions of Word can not always read documents produced using newer versions of Word. Thanks, Miya Woolfalk -- Miya Woolfalk Ph.D. Student Harvard University Government and Social Policy

15 years, 2 months

[gov2001-l] problem sets

by plam＠fas.harvard.edu

Hi all, Don't forget, your problem sets are due by tomorrow at 7 into your respective dropboxes. Local students, please bring a hardcopy of your writeup to whichever section you attend. The new problem set will be released tomorrow night at 9 pm. -- Patrick Lam Department of Government and Institute for Quantitative Social Science, Harvard University http://www.people.fas.harvard.edu/~plam

15 years, 2 months

[gov2001-l] LaTeX questions

by tom_sander＠Harvard.Edu

It's a steep learning curve this week between R and LaTeX . I successfully downloaded LaTeX through the ProTexnic Center. And tried using it. If people have used LaTeX before, is there an easy way to 1) preview what you are doing (without all the formating codes) 2) how to print from LaTeX into a PDF without all the formatting codes? I think if I could figure out #1 I could figure out #2, but if I try to do a PDF now it keeps all the formatting codes in. 3) create a table. When I do Insert - Table I get a lot of code like \begin \table (etc.) but I don't see any choices other than 1 or 2 columns and nothing that enables me to see the table as I'm creating it. Any one out there an experienced LaTeX user? Many thanks. Best. Tom

15 years, 2 months

[gov2001-l] Math Preceptor

by woolfalk＠fas.harvard.edu

Hi All, I wanted to let you all know about a great resource in the Government department. Pedram Safari (safari at fas.harvard.edu) is a math preceptor and he is available Monday, Wednesday and Friday from 11am-12pm in CGIS S310 to answer any questions you may have about math (e.g. integration, derivatives, optimization) and probability theory (e.g. probability distributions, conditional probability, MCMC methods). He is happy help students gain a better understanding of the math and theory underlying many of the topics we cover in Gov 2001. So, you should all feel free to stop by his office during those hours. Best, Miya -- Miya Woolfalk Ph.D. Student Harvard University Government and Social Policy

15 years, 2 months

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Gov2001 February 2009