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From |
Viktor Emonds <Viktor.Emonds@soc.kuleuven.be> |

To |
"statalist@hsphsun2.harvard.edu" <statalist@hsphsun2.harvard.edu> |

Subject |
st: RE: RE: i-1 in forvalues loop |

Date |
Tue, 18 Oct 2011 17:24:54 +0200 |

Thanks, dr. Cox, your correction solved the problem. Sorry for bothering you with the second email! Viktor --------------------------------- Sorry, Viktor, you're hoping for more than I can promise. I promise only to comment on what Stata problems you raise that I can understand. I've not tested your code -- manifestly I don't have your data -- but I see no reason why your code shouldn't run with my correction. Did you try that? I don't see any adding of intervals in your code. Nick ----------------------------------------------- Let me try to explain again: I have a file with schools and I know the number of students in the target population. I have everything neatly sorted and for sampling, I just need to give each school a chance poportional to the number of students in the target year in that school on getting selected, determinate a random starting point to make my first pick and add a constant interval. In the loop with bal, I basically try to draw the 'winning numbers' by taking the constant (bal1) and adding the interval (3166.467), storing the new constant in bal2, bal3 ....bal15. The way I envisioned doing this was by running a loop for bal2-bal15, adding the interval to the value of the previous bal (the i-1th bal). Is there a way to do so? Best, Viktor ______________________________ I don't understand what you are trying to do. I comment only on obvious Stata problems. `i-1' would only work if "i-1" were the name of a local macro, but it can't be such a name, as minus signs are not allowed in Stata names. gen bal`i' = bal`=`i'-1' * 3166.467 would at first sight work as then Stata knows to evaluate the expression `i' - 1 on the fly. Your code largely consists of putting constants into variables, which is legal but not especially good style. Note that gen lotto=sum(studentsj3) //sum of target population produces a _cumulative_ sum: only in the last observation will this be the actual sum, as your comment implies. Whether the comment or the code is what you want only you can say. Nick ________________________________________ Van: Viktor Emonds Verzonden: dinsdag 18 oktober 2011 15:55 Aan: statalist@hsphsun2.harvard.edu Onderwerp: i-1 in forvalues loop Hey, I am trying to draw a sample with random start, fixed interval systematic sampling procedure in each explicit stratum. The data in each stratum are already sorted by all the implicit stratifiers with serpentine sorting for a variable of particular interest. Now I just need to do the actual sampling and tried to start by doing the following: use ethnicframe31 //the specific explicit stratum gen lotto=sum(studentsj3) //sum of target population egen bal1= mean(3166.4667*runiform()) //random starting point forvalues i=2/15 { //Draw ' lotto balls' by adding the fixed interval gen bal`i'= bal`i-1'*3166.4667 } gen winnaar=0 //Identify ' winning' schools forvalues i=1/15{ replace winnaar=1 if inrange(bal`i',lotto[_n-1],lotto) } Apparently, the `i-1' in the first loop is not understood. What am I doing wrong here? Thanks in advance! Best, Viktor * * 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/

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