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RE: st: RE: FWD: poisson regression on aggrgregated data |

Date |
Tue, 10 Feb 2009 01:32:28 +0000 |

Thank you very much Kieran for your response. I will difinetly read your paper. Now my question is if the predicted rate in my final poisson model for example for time_since_start_cat=3 and year_start_cat=2 is 0.076 or 76 per 1000 person years , what will be the predicted rate : for example for year_start=2003 (whitch has been coded as year_start_cat=2) and year_since_start=3_4 (which has been coded > as year__since_start_cat=3) Will it be 0.076 person years? If not how can I have the predicted rate for ungrouped data using my poisson model. Many thanks again, Shell > Subject: RE: st: RE: FWD: poisson regression on aggrgregated data > Date: Tue, 10 Feb 2009 06:28:51 +0900 > From: kamccaul@meddent.uwa.edu.au > To: statalist@hsphsun2.harvard.edu > > OK, I see. > > You have the year that treatment started: 1997,1998,1999,...,2008 > which you have coded as: > year_start_cat = 1 if year_start=1997 and > year_start_cat = 2 if year_start=1998,1999,...,2008 > > You have time since the treatment started (time_since_start):0_1, 1_2, > 2_3,...,Max > coded as: > time_since_start_cat = 1 if time_since start = 0_1 . > time_since_start_cat = 2 if time_since start = 1_2 > time_since_start_cat = 3 if time_since start = 2_3,...,Max > > Then you modelled the incidence rates using these covariates and now you > want to predict the rates in each of the calendar years that treatment > started (1997,1998,1999,...,2008) and in each of the years since > treatment started (0_1, 1_2, 2_3,...,Max). > > Your model is assuming that the rate in the treatment years 1998 to 2008 > is the same. Similarly, it is assuming that after two years of > follow-up have elapsed, the rate is the same; constant with time since > treatment started. In fact, it is assuming that this constant rate is > the same for all treatment years, 1998 to 2008. > > If these assumptions are correct, then you could use the model to > predict the rates, but you would need to provide some evidence that they > are correct. > > If you have sufficient data, you could use -strate- to generate the > rates for year_start and time_since start to see if your assumptions are > essentially correct. > > strate year_start time_since start > > This would give you the annual incidence rates since treatment started > and you could graph these for each calendar year. I did something > similar to this in a study of second primary melanoma rates: > McCaul et al. The incidence of second primary invasive melanoma in > Queensland, 1982-2003. Cancer Causes Control 2008; 19(5):451-8. > > Alternately, you could go back to your original data and use > Kaplan-Meier to generate hazard curves by calendar year of treatment. > These should be constant three or more years after treatment and they > should be similar for 1998 through to 2008. > > ______________________________________________ > Kieran McCaul MPH PhD > WA Centre for Health & Ageing (M573) > University of Western Australia > Level 6, Ainslie House > 48 Murray St > Perth 6000 > Phone: (08) 9224-2140 > Fax: (08) 9224 8009 > email: kamccaul@meddent.uwa.edu.au > http://myprofile.cos.com/mccaul > http://www.researcherid.com/rid/B-8751-2008 > ______________________________________________ > The fact that no one understands you doesn't make you an artist. > > -----Original Message----- > From: owner-statalist@hsphsun2.harvard.edu > [mailto:owner-statalist@hsphsun2.harvard.edu] On Behalf Of [Redacted] > Sent: Monday, 9 February 2009 9:30 PM > To: statalist@hsphsun2.harvard.edu > Subject: RE: st: RE: FWD: poisson regression on aggrgregated data > > Dear Kieran > > > No I am not modeling mortality rates, I am modeling the incident of > experiencing an event by patients using these 2 covariates: > > year_start (year of starting treatment): 1997,1998,1999,...,2008 > time_since_start:0_1, 1_2, 2_3,...,Max > > My original data was not in aggregated form, and patients experienced > the event (1) or not (0). Then I splitted the follow up time in one year > periods and coded year_start,1997 as 1 and 1998+ as 2 and time_since > start ,0_1 as 1, 1_2 as 2 and 2+ as 3. then aggregated data using these > coded covariates: > > strate year_start_cat time_since_start_cat > > saved the output, and used poisson on _D (count of events in each > group)-created by strate-, above 2 coded covariates (year_startcat, > time_since_startcat) and the exposure that would be created aggregated > follow up time _Y ,and then predicted number of events and incident > rates in each group using predict. > > Now I would like to use the coefficients of this fitted poisson model > and have the predicted incident rates in disaggregated data (for > year_start and time_since_start before grouping them) > > for example the incident rate for year_start=2003 (whitch has been > coded as year_startcat=2) and year_since_start=3_4 (which has been coded > as year__since_startcat=3) > > Would it be correct if I use the same predicted incident rate from > poisson on grouped data (1998+ and 2+) and use it for above example or > each case in this group or in this case more events than really is will > be predicted? > > Many thanks, > Shell > > >> Subject: st: RE: FWD: poisson regression on aggrgregated data >> Date: Mon, 9 Feb 2009 04:09:31 +0900 >> From: kamccaul@meddent.uwa.edu.au >> To: statalist@hsphsun2.harvard.edu >> >> . >> >> It's not clear from this description what you are modelling. Is it >> mortality rates? >> Second, when you say that you have used aggregated data, is this data >> that you have aggregated or was the data already in aggregated form? >> >> >> >> ______________________________________________ >> Kieran McCaul MPH PhD >> WA Centre for Health & Ageing (M573) >> University of Western Australia >> Level 6, Ainslie House >> 48 Murray St >> Perth 6000 >> Phone: (08) 9224-2140 >> Fax: (08) 9224 8009 >> email: kamccaul@meddent.uwa.edu.au >> http://myprofile.cos.com/mccaul >> http://www.researcherid.com/rid/B-8751-2008 >> ______________________________________________ >> The fact that no one understands you doesn't make you an artist. >> >> -----Original Message----- >> From: owner-statalist@hsphsun2.harvard.edu >> [mailto:owner-statalist@hsphsun2.harvard.edu] On Behalf Of Martin > Weiss >> Sent: Sunday, 8 February 2009 7:55 PM >> To: statalist@hsphsun2.harvard.edu >> Subject: st: FWD: poisson regression on aggrgregated data >> >> <> >> >> Dear [Redacted], >> >> short answer: I do not know! BTW, it is not clear to me why you want > to >> tap >> only my wisdom when you can have the entire list. So I am forwarding >> this >> topic to the list for you... >> >> >> HTH >> Martin >> _______________________ >> >> >> Dear Martin >> >> I would like to ask the following question. >> >> I have used poisson regression on aggrgregated data with 2 covariates >> (in a >> cohort of HIV positive patients) >> >> 1.year of starting 3+ antiretroviral treatment (1997, 1998+) >> 2.time since starting 3+antiretrovirals (0-1, 1-2, 2+) >> >> and I have predicted incident rates in this aggregated data using >> predict >> option after the poisson model. >> >> Now my question is if I want to have predicted incident rates for >> patients >> starting 3+ arvs at 2000 and time since starting 3+ arvs , 3_4 years >> is it correct to use the same predicted incident rate obtained for >> aggregated data and in this example use predicted incident rate for >> 1998+ >> and 2+? >> >> It would be greatly appreciated if you could answer my question, > Please >> let >> me know if you would like me to provide more details. >> >> Thank you very much in advance, >> >> Kind regards, >> Shell >> >> * >> * 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/ > _________________________________________________________________ > News, entertainment and everything you care about at Live.com. Get it > now! > http://www.live.com/getstarted.aspx > * > * 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/ _________________________________________________________________ Invite your mail contacts to join your friends list with Windows Live Spaces. It's easy! http://spaces.live.com/spacesapi.aspx?wx_action=create&wx_url=/friends.aspx&mkt=en-us * * 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/

**Follow-Ups**:**RE: st: RE: FWD: poisson regression on aggrgregated data***From:*"Kieran McCaul" <kamccaul@meddent.uwa.edu.au>

**References**:**st: FWD: poisson regression on aggrgregated data***From:*"Martin Weiss" <martin.weiss1@gmx.de>

**st: RE: FWD: poisson regression on aggrgregated data***From:*"Kieran McCaul" <kamccaul@meddent.uwa.edu.au>

**RE: st: RE: FWD: poisson regression on aggrgregated data***From:*[Redacted]

**RE: st: RE: FWD: poisson regression on aggrgregated data***From:*"Kieran McCaul" <kamccaul@meddent.uwa.edu.au>

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