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From |
"Nick Cox" <n.j.cox@durham.ac.uk> |

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

Subject |
st: RE: egen or other methods to calculate consecutive row totals? |

Date |
Mon, 3 Mar 2003 19:58:12 -0000 |

Alexandra de Montrichard > > I am somewhat new to stata and I need some help with a > problem I can't > seem to resolve. > > I am working with a database of students for whom I have quarterly > grades for 5 years (1995-2000). I also have the start & > completion date > for a class that all students took a one point during those > five year. I > need to figure out how many quarters of grades I have for > each student > before & after they took this class & how many are > consecutive quarters > of grades. I've created a 0-1 variable for each quarter (0 if the > student did not get any grades that quarter, 1 if they received a > grade), converted the class start & exit date into quarter > format & used > egen to count of the number of quarters in which each > student received > grades > . egen byte gradenbr = neqany (grade951-grade004), v (1) > However, I now need to figure out a way of counting the number of > quarters with grades both before & after the class as well > as a way to > know how many consecutive quarters with grade I have after > completion of > the class. I though I could use egen combined with if to create a > gnbrpost variable of the number of quarters with grades > after completion > of the class: > . egen byte gnbrpost = neqany (grade951-grade004) if (exitdq== > q(1995q1)), v (1) > . egen byte gnbrpost = neqany (grade952-grade004) if (exitdq== > q(1995q2)), v (1) > . egen byte gnbrpost = neqany (grade953-grade004) if (exitdq== > q(1995q3)), v (1) etc..... > > but I can't figure out how to replace the gnbrpost variable > each time I > run a new egen calculation plus I'm sure there must be a > better way of > doing this, which would also allow me to know how many consecutive > quarters of grades I have. In one sentence: -reshape- to -long- and convert your structure into a panel data structure. Then use e.g. -tsspell-. from SSC. Your columns grade951-grade004 should be mapped into one variable -grade-, another -quarter- and another -student-. . reshape long grade, i(student) j(quarter) string -quarter- as a string variable is not handy for time series work. . gen year = real( cond(substr(quarter,1,1)=="9", "19" + substr(quarter,1,2), "20" + substr(quarter,1,2)) ) . gen qtr = real(substr(quarter,-1,1)) . gen q = yq(year, qtr) . format q %tqq_Cy . tsset student q Now you need to divide each student's record into before, during and after taking a course. One way to do it is using -tsspell- from SSC. There are several examples in its help. Nick n.j.cox@durham.ac.uk * * For searches and help try: * http://www.stata.com/support/faqs/res/findit.html * http://www.stata.com/support/statalist/faq * http://www.ats.ucla.edu/stat/stata/

**References**:**st: egen or other methods to calculate consecutive row totals?***From:*Alexandra de Montrichard <ademontr@attbi.com>

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