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From |
"Ariel Linden, DrPH" <ariel.linden@gmail.com> |

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

Subject |
re: Re: st: replicating 2 X 2 data from a paper |

Date |
Wed, 3 Apr 2013 09:38:22 -0400 |

Thanks Adam and David. It's nice to know that I am not crazy. I also tried cci and iri and obviously got the same results as Adam. I am somewhat surprised that a paper in the Archives of Internal Medicine would not be scrutinized more closely by statistical reviewers. Date: Tue, 2 Apr 2013 21:04:43 -0400 From: Adam Olszewski <adam.olszewski@gmail.com> Subject: Re: st: replicating 2 X 2 data from a paper Hi Ariel, The footnote in the table says "Percent differences were calculated by dividing the absolute difference between groups by the usual care group value." So, the "Treatment difference" = (158-152)/152 = .03947368 How they got the P-value of 0.45 I have no idea. cci 152 158 95 96 gives 0.87 iri 152 158 95 96 gives 0.80 AO Date: Tue, 2 Apr 2013 22:21:47 -0400 From: David Hoaglin <dchoaglin@gmail.com> Subject: Re: st: replicating 2 X 2 data from a paper Hi, Ariel. As presented, those data would not be compatible with a 2 X 2 table format. If one were classifying the subjects in each group according to whether they had a hospitalization at (prior to?) baseline, the result would form a 2 X 2 table, to which one could apply a chi-squared test or an exact test. If I'm interpreting the numbers correctly (it's not convenient for me to look up the article), the 96 subjects in the treatment group had a total of 152 baseline hospitalizations among them, and the 95 subjects in the control group had a total of 158 baseline hospitalizations. Those data yield rates (as you calculated), not proportions. It seems that the authors did not document their statistical analysis adequately. A comparison of two rates may involve a chi-squared test. I don't recall. Treating it as Poisson regression would seem to be overkill. David Hoaglin On Tue, Apr 2, 2013 at 8:16 PM, Ariel Linden, DrPH <ariel.linden@gmail.com> wrote: > Hi Fellow Statalisters, > > I am having a problem conceptualizing how to replicate data from a paper I > am reading (Bourbeau et al. 2003).* They have two groups (treatment = 96, > control= 95) who had 152 and 158 baseline hospitalizations, respectively. > > They describe in the text: " the comparison of the proportion of hospital > admissions or emergency department and medical visits was based on the chi2 > test. The Fisher exact test was used when the frequencies were small. > Percent difference effects of the intervention were calculated by dividing > the absolute difference between the intervention and usual care group > values." > > The table (table 2) shows the difference as 3.9% and a p-value of 0.45. > > So with this minimal information, I'd like to replicate the results, perhaps > using a 2 X 2 table format and test with chi2. > > My basic math (see below) does not seem to replicate the difference they > present. I get close using (treat-usual)/treat, but that is not consistent > with their text. Using a rate difference, I get something completely > different. In any case, I am not sure if there is a simple way to reproduce > these results consistent with how they claim to get there... > > usual treat (treat-usual)/treat > admits 152 158 0.038 > N 95 96 > admits/N 1.6 1.65 0.046 > > * Bourbeau JB, et al. Reduction of hospital utilization in patients with > chronic obstructive pulmonary disease. Arch Intern Med 2003: 163:585-591. > > Any help would be appreciated! > > Ariel * * 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: Re: st: replicating 2 X 2 data from a paper***From:*David Hoaglin <dchoaglin@gmail.com>

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