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From |
"Seed, Paul" <paul.seed@kcl.ac.uk> |

From |
"Joseph Coveney" <jcoveney@bigplanet.com> |

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

Subject |
st: Re: sensitivity and specificity after xtgee |

Date |
Mon, 17 Sep 2012 22:01:34 +0100 |

Date |
Mon, 17 Sep 2012 14:33:51 +0900 |

Mohammadreza Mohebbi wrote: Is there any post-estimation option after running xtgee/ xtlogit (for binary longitudinal regression) for calculating sensitivity, specificity, positive and negative predictive values, positive and negative likelihood ratios and ROC curve? I used xtgee to fit binary regression for wheez syndrome with 3 measurements (baseline, first year and second year follow-ups) with PD20 as exposure and broadcat and smoker_current as covariates: xtset h_id h_int_no xtgee wheez_symp pd_20_base i.broadcat smoker_current , corr(exchangeable) fam(binom) link(log/logit) eform robust - -------------------------------------------------------------------------------- The roc areas are easy: predict pred1 if h_int_no == 1, mu roctab wheez_symp pred1 And likewise for visits 2 and 3. My user-written command -diagt- will calculate all the other indicators he wants for a given yes/no test, with simple yes/no : He can install it in the usual way, starting with findit diagt It will also do a few other things, such as calcualte confidence intervals (assuming simple random samples at each time point, and estimate predictive values for different case mixes/disease prevalences. However, he needs to decide what probability of an event he wants to consider as positive. 50% is a common default value; but in practice (clinical settings), I have found much lower values are important (e.g. 3%, 5%, 20%), depending on the relative costs associated with the tow kinds of errors (false positive and false negative decisions). gen test_pos1 = pred1 >= .2 if h_int_no == 1 diagt wheez_symp test_pos1 Paul T Seed MSc CStat CSci, Senior Lecturer in Medical Statistics, King's College London, Division of Women's Health * * 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/

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