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From |
Steve Samuels <sjsamuels@gmail.com> |

To |
statalist@hsphsun2.harvard.edu |

Subject |
Re: st: RE: comparison of agreement plot for non-Normal data |

Date |
Thu, 8 Apr 2010 10:44:21 -0400 |

"This does not produce the same 95% CI as the equation from the double regression (recommended in the paper mentioned above)" b0 + b1A ą 1.96 * residual SD from the regression." I assume you mean: b0 + b1A +/ 1.96 * residual SD This is not the equation for a confidence interval. The variability of a predicted mean depends on the distance of the predictor variable (A) from the sample mean. . See the correct equation in the section on linear regression of any introductory text. Secondarily, -twoway lfitci- will use a t-multiplier not a z- (Gaussian) multiplier Steve > Pinto, Daniel > > I am analyzing the results of a method comparison study assessing agreement between two methods of capturing health service use and costs, N=50. Due to the small sample size and the analysis of cost data my distribution is non-Normal. I believe that Bland-Altman plot is the best statistic to use except that it assumes a Normal distribution. To address non-Normality Bland and Altman recommend using a double-regression half-Normal distribution method in the following paper: Bland JM, Altman DG. Measuring agreement in method comparison studies. Stat Methods Med Res. 1999 Jun;8(2):135-60. > > I have attempted the performance of this method in STATA 10, plotting the residuals of the difference in GP count against the mean of the GP count. > > regress gpcntdif meangpcnt > > predict gpcntdifresid, resid > > regress gpcntdifresid meangpcnt > > I have tried to produce the plot including 95% CI using: twoway lfitci gpcntdifresid meangpcnt, stdf || scatter gpcntdifresid meangpcnt > > This does not produce the same 95% CI as the equation from the double regression (recommended in the paper mentioned above): > b0 + b1A ą 1.96 * residual SD from the regression. > > Although I can calculate the 95% CI using the equation I am unable to apply the 95% CI lines to the B-A plot. Is there anyway how to do this? > > > * > * 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/ > -- Steven Samuels sjsamuels@gmail.com 18 Cantine's Island Saugerties NY 12477 USA Voice: 845-246-0774 Fax: 206-202-4783 * * 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: comparison of agreement plot for non-Normal data***From:*"Pinto, Daniel" <dpinto@regis.edu>

**st: RE: comparison of agreement plot for non-Normal data***From:*"Nick Cox" <n.j.cox@durham.ac.uk>

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