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From |
Michael McCulloch <mm@pinest.org> |

To |
statalist@hsphsun2.harvard.edu |

Subject |
Re: st: comparing -ltable- and -sts list- |

Date |
Sun, 2 Nov 2008 21:25:30 -0800 |

Thank you Philip for the very helpful explanation. Michael

MichaelI think that to perform a test *at a particular time*, as opposed toan overall (logrank style) test, using the K-M estimator you need to(i) estimate the S(t) and the Greenwood variance for each group atthe chosen time(ii) perform a z test Step (i) can be done by sts list: . sts list , by(drug) at(0,2) failure _d: died analysis time _t: studytime Beg. Survivor Std.Time Total Fail Function Error [95%Conf. Int.]------------------------------------------------------------------------------- drug=1 0 0 0 1.0000 . . . 2 18 3 0.8500 0.0798 0.6038 0.9490 drug=2 0 0 0 1.0000 . . . 2 0 0 1.0000 . . . drug=3 0 0 0 1.0000 . . . 2 0 0 1.0000 . . . -------------------------------------------------------------------------------Note the syntax of the -at()- option. Had I just put -at(2)- Statawould have given me its 2 chosen times, not necessarily t=2. (Tryit and see!)Then you can retrieve S(t=2) for each of the two groups of interestand the SEs and thus calculate the Greenwood estimate of thevariance of the difference in S(t). The z test follows...Step (ii): z = (S1(t=2) - S2(t=2)) / [ sqrt(Var(S1(t=2) + Var(S2(t=2))]where Var(S(t=2) is the square of the SE for the respective group atthe desired time.whence you can use the -normal()- function to get your P value.Doesn't look like your particular data (at t=2) will support thistest - we only get an estimate for drug=1. But the above is thegeneral idea. Someone else may know of a more direct way.Phil At 11:33 AM 3/11/2008, you wrote:Thanks Phil.Is there a way to use -sts list- to statistically compare the2-year survival rates between two groups? I notice that the-compare- option simply places them next to each other without astatistical test.MichaelMichael use the -noadjust- option on -ltable- from -help ltable- :noadjust suppresses the actuarial adjustment for deaths andcensored observations. The default is to consider theadjusted number at risk at the start of the interval to betotal at the start minus (the number dead or censored)/2.If noadjust is specified, the number at risk is simply thetotal at the start, corresponding to the standardKaplan-Meier assumption. noadjust should be specifiedwhen using ltable to list results corresponding to thoseproduced by sts list. Phil At 09:51 AM 3/11/2008, you wrote:Dear Statalist members,I had the impression that both -ltable- and -sts list- would listthe survivor function per failure period. However, they giveslightly different answers. In the example below, for drug3-ltable- shows survival at 24 months as 77.14%, whereas -stslist- says it's 64.29%sysuse cancer.dta, clear sts list, by(drug) ltable _t died, by(drug) Could anyone help me to clarify this? -- Best wishes, Michael McCulloch Pine Street Foundation 124 Pine St., San Anselmo, CA 94960-2674 Tel: (415) 407-1357 Fax: (415) 485-1065 mcculloch@pinestreetfoundation.org www.pinestreetfoundation.org * * 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/Philip Ryan Professor, Discipline of Public Health Director, Data Management & Analysis Centre Associate Dean (IT) Faculty of Health Sciences postal address: Discipline of Public Health Mail Drop DX650 511 University of Adelaide 5005 South Australia location: Level 6, Room 6-18 Bice Building Royal Adelaide Hospital North Terrace Adelaide tel +61 8 8303 3570 fax +61 8 8223 4075 http://www.public-health.adelaide.edu.au/ CRICOS Provider Number 00123M ----------------------------------------------------------- This email message is intended only for the addressee(s) and contains information that may be confidential and/or copyright. If you are not the intended recipient please notify the sender by reply email and immediately delete this email. Use, disclosure or reproduction of this email by anyone other than the intended recipient(s) is strictly prohibited. No representation is made that this email or any attachments are free of viruses. Virus scanning is recommended and is the responsibility of the recipient. * * 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/Philip Ryan Professor, Discipline of Public Health Director, Data Management & Analysis Centre Associate Dean (IT) Faculty of Health Sciences postal address: Discipline of Public Health Mail Drop DX650 511 University of Adelaide 5005 South Australia location: Level 6, Room 6-18 Bice Building Royal Adelaide Hospital North Terrace Adelaide tel +61 8 8303 3570 fax +61 8 8223 4075 http://www.public-health.adelaide.edu.au/ CRICOS Provider Number 00123M ----------------------------------------------------------- This email message is intended only for the addressee(s) and contains information that may be confidential and/or copyright. If you are not the intended recipient please notify the sender by reply email and immediately delete this email. Use, disclosure or reproduction of this email by anyone other than the intended recipient(s) is strictly prohibited. No representation is made that this email or any attachments are free of viruses. Virus scanning is recommended and is the responsibility of the recipient. * * 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/

**References**:**st: comparing -ltable- and -sts list-***From:*Michael McCulloch <mm@pinest.org>

**Re: st: comparing -ltable- and -sts list-***From:*Philip Ryan <philip.ryan@adelaide.edu.au>

**Re: st: comparing -ltable- and -sts list-***From:*Michael McCulloch <mm@pinest.org>

**Re: st: comparing -ltable- and -sts list-***From:*Philip Ryan <philip.ryan@adelaide.edu.au>

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