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From |
[Redacted] |

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<statalist@hsphsun2.harvard.edu> |

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

Date |
Tue, 10 Feb 2009 06:54:52 +0000 |

Thanks a lot Kieran for your response. and I am very sorry when I sent my last email I hadn't seen this email of yours yet. All the best, Shell ---------------------------------------- > Subject: RE: st: RE: FWD: poisson regression on aggrgregated data > Date: Tue, 10 Feb 2009 12:05:02 +0900 > From: kamccaul@meddent.uwa.edu.au > To: statalist@hsphsun2.harvard.edu > > The model can only predict from what you have given it. If you group > together all the calendar years from 1998 to 2008, then what the model > is predicting is the overall rate for these years combined. If you are > confident that there is little variation in the rate by calendar year, > then it would be OK to model it this way. > > On the other hand, if there is variation in the rates by calendar year, > then the average rate over all years will not be a good estimate of the > rates by each calendar year. > > > > ______________________________________________ > 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: Tuesday, 10 February 2009 10:32 AM > To: statalist@hsphsun2.harvard.edu > Subject: RE: st: RE: FWD: poisson regression on aggrgregated data > > > > 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.a > spx&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/ > > > > * > * 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/

**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>

**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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