However, it is definitely available after the somersd command, downloadable from ssc. I believe you need to use somers d, sometimes abbreviated as dyx or dxy, using the package somersd to compute the confidence interval. Harrell s c statistic five potential alternate staging systems were generated at age cutpoints in 5year increments from 35 to 70 years, and tested for model discrimination harrell s c. Conventional measures of predictive ability need modification for this design. The acci scores provided better discriminatory ability with a smaller akaike information criterion and greater harrell s c statistic for 3year overall survival compared to the charlson comorbidity index or elixhauser comorbidity index. Stata module to compute harrell s c index for flexible parametric models, statistical software components s457227, boston college department of economics. The equivalent statistic is harrell s c, which you can calculate using estat concordanceif you have a large dataset youll find that estat concordance takes a long time to run, in which case you might want to use somersd, a stata. Are there any suggestions for creating a nomogram for the prediction of cancer patient survival. The somersd package, downloadable from statistical software. How to compare harrell cindex from different models in. So the next question is to compare the discrimination ability of the three models. Harrell s c index is not available as a postestimation statistic after stcrreg or any parametric survival model. If you use stata, you get the results immediately after just enter the.
This family is implemented in stata by using the somersd package, which can be downloaded from statistical software. We show how harrell s c index, roystons d, and the categorybased and continuous versions of the net reclassification index. How can i calculate harrells c for a proportional hazards. Harrell s c and somers d are members of the kendall family of rank parameters. Need to calculate harrell s c statistics or whats know by c index. Stata module to compute harrells cindex for flexible. However, lroc provides area under roc curve as point estimate.
Stata provides the estat concordance command to calculate the rank parameters harrell s c and somers d as measures of the ordinal predictive power of a model. I tried the stcstat program that i found online but that doesnt seem. Bootstrapping harrell s c problem with freezing model to establish optimism stepwise etc. Statistical software components from boston college department of. I really appreciate your help in calculating a c index. Statistical analysis was performed using stata software version 12. Patrick royston additional contact information patrick royston. Note that, if you want harrell s c to have confidence limits that can be taken seriously, then the hazard ratio should be derived using outofsample prediction from a cox model fitted to a different dataset from the dataset in which you estimate harrell s c. However, i have written a stata journal article about how to carry out such a procedure in stata using somersd, and the issues involved newson, 2010. On april 23, 2014, statalist moved from an email list to a forum. Ive been using lroc command following logit to calculate c statistics. The stata journal comparing the predictive power of. Pdf comparing the predictive powers of survival models.
Mrc clinical trials unit statistical software components from boston college department of economics. This variable might be calculated after a cox regression by using the predict command with the hr option. Casecohort studies are increasingly used to quantify the association of novel factors with disease risk. Need to calculate harrells cstatistics or whats know by. Greg heath on 7 sep 2014 i am doing survival analysis using neural networks, i would like to calculate harrell s c index as. Assessment of discrimination in survival analysis c. I dont know why harrell s c is not available afert parametric survival model. Is there any stata code for calculating the c index also known as c statistics and concordance statistics, for fine gray i found an r package that does this but i have no idea how to do it in stata. In a dataset with survival event, i calculated harrell c index from three different models.
Stata programs of interest either to a wide spectrum of users e. The concordance probability is a widely used measure to assess discrimination of prognostic models with binary and survival endpoints. Science citation index expanded also known as scisearchr. I posted some sample code below, including a test data set to act like an external validation set. Harrell s c statistic is not directly available in proc phreg or other sas. Derivation and assessment of risk prediction models using. Stata module for harrell davis estimator of quantiles, statistical software components s449601, boston college department of economics. Emphasis is given to maximizing the use of information, avoiding statistical pitfalls, describing. This module should be installed from within stata by typing ssc install. Cindex confidence interval statalist the stata forum. Could anyone kindly suggest the method to compare the harrell c index. Comparing the predictive powers of survival models using harrell s c or somers d article pdf available in stata journal 103. Stata postestimation command estat concordance see st stcox.
How can i calculate the area of roc curve of a cox model. Domantas sabonis faces off against montrezl harrell in the first round of the nba 2k players tournament. Stata provides the estat concordance command to calculate the rank parameters harrells c. Comparing the predictive powers of survival models using harrells c or. Im also not able to use the estat concordance command suggested. Comparing the predictive power of survival models using harrells c or somers d. I have a followup question regarding the c statistics.
Statistical thinking this blog is devoted to statistical thinking and its impact on science and everyday life. Computing cindex for an external validation of a cox ph. The sas system provides biologists with a flexible, easy to use software package for data analysis. I discriminated the nomogram with harrell s c index but now i am stuck. The stata 9 version of somersd uses the mata language for improved computational e. Requests for stata code are offtopic here and the emphasis on stata code would stretch people more accustomed to other software. If reasonable to ignore this, frank harrells rms package, as mentioned. This module should be installed from within stata by typing ssc install stcstat2. How can i calculate concordance cstatistic cindex for clustered. On the c statistics for evaluating overall adequacy of risk prediction procedures with censored survival data.
On the cstatistics for evaluating overall adequacy of. Montrezl harrell s unrivaled work ethic stood out at an early age. Reading the help file says to use the transf c option to transform d to the probability scale of the c. The ageadjusted charlson comorbidity index is a better. Sas code or macro for calculating cindex and roc curves for cox models. I tried the stcstat program that i found online but that doesnt. Sas code or macro for calculating cindex and roc curves. Regression modeling strategies presents fullscale case studies of nontrivial datasets instead of oversimplified illustrations of each method. How can i calculate concordance c statistic c index for clustered survival data. Are there any suggestions for creating a nomogram for the. Bootstrapping harrell s c problem with freezing model to establish optimism. Comparing the predictive powers of survival models using harrells. However, no confidence limits or p values are provided to compare the predictive power of distinct models.
The preoperative neutrophil to lymphocyte ratio is a. Id like to be able to calculate the cstatisticcindex for my proc phreg model. Concordance for prognostic models with competing risks. Comparing the predictive power of survival models using harrell s c or somers d. I wonder if there is a command or a method in stata that can calculate the point estimate and 95% confidence interval of c. We used the harrells cindex 27 to compare tbs and frailty. Assessment of discrimination in survival analysis c statistics, etc references. Concordance with timedependent covariates 6 april 17, 2007 individuals who are tied in both predictor and time are counted in ti and not in pi. These case studies use freely available r functions that make.
What would you have to do to account for clustering in the c index calculations or is it sufficient that i used the predicated survival values from a cluster adjusted proc phreg to then calculate. Can anyone help me to graphically represents the harrels c index in stata 14. Id like to be able to calculate the c statistic c index for my proc phreg model. Estimating harrell s optimism on predictive indices using bootstrap samples yinghui miao, ncire, san francisco, ca. In principle, the difference between 2 harrells c statistics can be. The somersd package, downloadable from statistical software components, can. Newson national heart and lung institute, imperial college london. Stata module to compute harrell s c index for flexible parametric models. Harrell s c parameters of these predictors, with respect to the outcome, and then make. Comparing the predictive powers of survival models using.
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