Notice: On April 23, 2014, Statalist moved from an email list to a forum, based at statalist.org.
| From | Zeynep Ozkok <zeynepozkok@gmail.com> |
| To | statalist@hsphsun2.harvard.edu |
| Subject | Re: st: RE: creating loops using combinations of variables |
| Date | Thu, 16 Feb 2012 13:10:58 +0100 |
Hi, Thank you very much for your comment Nick. Let me try to clarify the issue a bit by taking three variables as you suggested. The three variables are: var1, var2, and var3. What I would like to do is the following: Step 1: Generate two variables called lex1, and lex2 such that, lex1 = var1 and lex2= var2+var3 Generate two indices index1 and index2, such that: index1 = ln(1+ lex1) and index2 = ln(1+lex2) Run a regression of the following form: Y_i,s,t= alpha_i +alpha_s +alpha_t +beta*(index1)_i,t +lamda* (index2)_i,t + error_i,s,t Save the coefficients for index1 and index2, and the Rsquare. Clear lex1, lex2, index1, index2. Step 2: Generate two variables called lex1, and lex2 such that, lex1 = var2 and lex2= var1+var3 Generate two indices index1 and index2, such that: index1 = ln(1+ lex1) and index2 = ln(1+lex2) Run a regression of the following form: Y_i,s,t= alpha_i +alpha_s +alpha_t +beta*(index1)_i,t +lamda* (index2)_i,t + error_i,s,t Save the coefficients for index1 and index2, and the Rsquare. Clear lex1, lex2, index1, index2. Step 3: Generate two variables called lex1, and lex2 such that, lex1 = var3 and lex2= var1+var2 Generate two indices index1 and index2, such that: index1 = ln(1+ lex1) and index2 = ln(1+lex2) Run a regression of the following form: Y_i,s,t= alpha_i +alpha_s +alpha_t +beta*(index1)_i,t +lamda* (index2)_i,t + error_i,s,t Save the coefficients for index1 and index2, and the Rsquare. Clear lex1, lex2, index1, index2. Unfortunately the order of the variables included in the index measures are important. I should be able to tell which significant indices include which variables. To me that seems almost impossible when considering 27 variables. Is there a way to construct a loop to run this entire process? Thank you so much for all your help. Zeynep > On Thu, Feb 16, 2012 at 11:41 AM, Nick Cox <n.j.cox@durham.ac.uk> wrote: >> "All possible combinations" would usually mean, for 27 variables, 27 ways of selecting just one, comb(27, 2) = 351 ways of selecting two, ..., up to comb(27, 27) = 1 way of selecting them all. In total that means 2^27 - 1 ~ 10^8 combinations. That is, precisely, 134,217,727 combinations. >> >> My suggestion is to set aside the fact that you have 27 variables. Show us exactly what you would do with just 3 variables, say. >> >> Nick >> n.j.cox@durham.ac.uk >> >> Zeynep Ozkok >> >> I have a question on how to create loops for combinations of different >> variables. I have 27 variables that I would like to put in two different >> indices. >> >> The indices can be constructed in two steps: >> >> Lex1=sum(of different variables out of 27) this variable should be able >> to take on 1 to 27 variables, so it should allow for all possible >> combinations. It could be equal to only 1 variable, or it could be equal to >> the sum of different variables >> >> Index1 = ln (1+lex1) this index is then dependent on what values lex1 >> takes on >> >> Similarly >> >> Lex2 = sum (of all the variables that are not accounted in lex1) again this >> could take on one variable, or more than one depending on the structure of >> lex1. >> >> Index2 = ln(1+lex2) this index is once again dependent on what values lex2 >> takes on, which is dependent on the values that lex1 takes on. >> >> Then these two indices will simultaneously be used in fixed effects >> regressions as follows: >> >> Y_i,s,t= alpha_i +alpha_s +alpha_t +beta*(index1)_i,t +lamda* (index2)_i,t >> + error_i,s,t >> >> The loop must go on until all possibilities/ combinations are completed. I >> need to check the results of the beta and lamda coefficients and their >> corresponding rsquares for each regression. Since there are numerous >> possibilities in constructing each index I need to create a loop. However I >> don't even know how to start out a loop that depends on combinations of >> variables. Could you possibly help me out in writing and solving this >> problem? >> >> >> * >> * For searches and help try: >> * http://www.stata.com/help.cgi?search >> * http://www.stata.com/support/statalist/faq >> * http://www.ats.ucla.edu/stat/stata/ * * For searches and help try: * http://www.stata.com/help.cgi?search * http://www.stata.com/support/statalist/faq * http://www.ats.ucla.edu/stat/stata/