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From |
hind lazrak <hindstata@gmail.com> |

To |
statalist@hsphsun2.harvard.edu |

Subject |
Re: st: manual weighted average variable in panel data set |

Date |
Thu, 15 Nov 2012 18:36:17 -0800 |

The best things are the simplest, isn't it? Thanks for the help! Best, Hind On Thu, Nov 15, 2012 at 4:56 PM, Nick Cox <njcoxstata@gmail.com> wrote: > No loops are needed. > > . l id conc resid_time > > +--------------------------+ > | id conc resid_~e | > |--------------------------| > 1. | 20059 15.96 380 | > 2. | 20059 21.17 100 | > 3. | 20059 18.07 480 | > 4. | 20060 30 181 | > 5. | 20060 16.68 292 | > |--------------------------| > 6. | 20061 23.78 269 | > 7. | 20061 18.07 103 | > +--------------------------+ > > . bysort id : gen sumw = sum(resid_time) > > . by id : gen sumwc = sum(conc * resid_time) > > . by id : gen meanc = sumwc[_N] / sumw[_N] > > . l > > +-------------------------------------------------------+ > | id conc resid_~e sumw sumwc meanc | > |-------------------------------------------------------| > 1. | 20059 15.96 380 380 6064.8 17.55771 | > 2. | 20059 21.17 100 480 8181.8 17.55771 | > 3. | 20059 18.07 480 960 16855.4 17.55771 | > 4. | 20060 30 181 181 5430 21.77708 | > 5. | 20060 16.68 292 473 10300.56 21.77708 | > |-------------------------------------------------------| > 6. | 20061 23.78 269 269 6396.82 22.19901 | > 7. | 20061 18.07 103 372 8258.03 22.19901 | > +-------------------------------------------------------+ > > This code is too long for efficiency, but shows what I believe you > want. You can also generate sumwc / sumc if you wish. > > I didn't try to follow your code, but you're missing how -sum()- does > cumulative sums. > > See also _gwtmean from SSC (David Kantor). (I don't agree with his > advice to make it a substitute for Stata's code for -gmean()-.) > > Nick > > On Fri, Nov 16, 2012 at 12:33 AM, hind lazrak <hindstata@gmail.com> wrote: > >> I have a panel data set with the following variables: ID time_resid conc >> The repeated observations vary from 1 to 5 for each individual (ID). >> Each observation has a time period (time_resid) during which a >> pollutant concentration occurs (conc). >> Here is an excerpt of the data >> >> list id conc resid_time counter in 1/7, sepby(id) >> >> +-------------------------------+ >> id conc resid_~e counter >> ------------------------------------ >> 1. 20059 15.96 380 1 >> 2. 20059 21.17 100 2 >> 3. 20059 18.07 480 3 >> ------------------------------------ >> 4. 20060 30 181 1 >> 5. 20060 16.68 292 2 >> ------------------------------------ >> 6. 20061 23.78 269 1 >> 7. 20061 18.07 103 2 >> +------------------------------------+ >> >> I need to create a variable using time_resid and conc that computes >> the time-weighted average concentration for each ID. >> >> The steps that I took were to create variable product (equal to >> resid_time * conc) and then I have been trying to come up with a loop >> that would do the following: >> for each person, and each observation compute the time weighted >> average concentration =( sum of product / total resid_time up) until >> the time at which the observation occurs. >> >> Here's my code: >> *************************************** >> bysort id: gen counter = _n >> bysort id: gen product= resid_time*conc >> >> bysort id: gen time = resid_time if _n==1 | counter[_N]==1 >> bysort id: gen twa= conc if _n==1 | counter[_N]==1 >> qui su counter >> forval i=1/`r(max)' { >> bysort id: replace product= product+ product[_n-`i'] if _n!=1 >> bysort id: replace time= resid_time+ resid_time[_n-`i'] if _n=1 >> } >> bysort id: gen twa = product/time > * > * For searches and help try: > * http://www.stata.com/help.cgi?search > * http://www.stata.com/support/faqs/resources/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/faqs/resources/statalist-faq/ * http://www.ats.ucla.edu/stat/stata/

**Follow-Ups**:**Re: st: manual weighted average variable in panel data set***From:*Nick Cox <njcoxstata@gmail.com>

**References**:**st: manual weighted average variable in panel data set***From:*hind lazrak <hindstata@gmail.com>

**Re: st: manual weighted average variable in panel data set***From:*Nick Cox <njcoxstata@gmail.com>

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