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From |
Abekah Nkrumah <ankrumah@gmail.com> |

To |
statalist@hsphsun2.harvard.edu |

Subject |
Re: st: Cragg Donald tests |

Date |
Thu, 22 Mar 2012 14:19:15 +0000 |

Dear Karan, I have looked at Cameron and Trivedi's book and the understanding I get is that it depends on the number of endogenous regressors in your model. If you have only one regressor then the minimum eigen value derived will be the same as the Cragg-Donald F statistic. Thus you compare the F statistic to the thresholds you have stated in your mail which is actually the Stock and Yogo's thresholds. The principle is that you first decided on a tolerable bias level say 10% which in your calculation is 16.38 of the Stock and Yogo threshold. Thus if your F statistic is higher than the 16.38 then one can cautiously conclude that the instruments are not weak If you have more than one endogenous regressors say 2, then you will have two first stage and therefore 2 F statistics. You can then calculate the minimum eigen value of the two statistics which is then compared to the the Stock and Yogo threshold values. Remember that the minimum eigen value is calculated by stata. Remember also that theoretically this is based on the assumption of iid errors. Thank you very much and hope this helps Gordon On Thu, Mar 22, 2012 at 12:14 AM, Karan Nagpal <karan.nagpal1@gmail.com> wrote: > > I'm trying to test the strength of my instruments, but not sure how to > interpret the Cragg-Donald IV values. I implemented ivreg2, and > received the following output: > > Stock-Yogo weak ID test critical values: > 10% maximal IV size 16.38 > 15% maximal IV size 8.96 > 20% maximal IV size 6.66 > 25% maximal IV size 5.53 > > I'm not sure what I should be comparing these values to and how I can > use the "main output" to find the Cragg-Donald F statistic, which is > what stata advised. > > Thanks, > Karan > > * > * 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: Cragg Donald tests***From:*Karan Nagpal <karan.nagpal1@gmail.com>

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