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From |
"Carlo Lazzaro" <carlo.lazzaro@tin.it> |

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

Subject |
st: R: Spearman's rank correlation coefficient - power calculation |

Date |
Thu, 19 Jun 2008 09:19:25 +0200 |

Dear Theo, the following one is a temptative answer to your message. I assume I have 20 observations ordered in ranks (degrees of freedom (d_f) are 20-20=18, according to the hypothesis test formula for Spearman's rank correlation coefficient). Ho to be tested is rho=0. I have calculated a random Spearman's ranK correlation coefficient, t (ts) and then the p-value. ....................begin example...................... set obs 1 g r_Spearman=1*uniform() g d_f=(20-2) g ts= r_Spearman*[(20-2)/(1-(-r_Spearman^2))]^.5 g p_value=ttail(d_f, ts) ...................end example....................... HTH and Kind Regards, Carlo -----Messaggio originale----- Da: owner-statalist@hsphsun2.harvard.edu [mailto:owner-statalist@hsphsun2.harvard.edu] Per conto di Theo Serge Inviato: giovedì 19 giugno 2008 8.24 A: statalist@hsphsun2.harvard.edu Oggetto: st: Spearman's rank correlation coefficient - power calculation Dear Statalist, I would be grateful if you could help me on a problem: Having submitted an article to a Journal, the reviewers asked me for power calculation on a Spearmanʼs rank correlation coefficient. This happened although I had been very careful with the interpretation of negative findings in the manuscript. Moreover, Spearmanʼs rank correlation coefficient was the appropriate choice for the univariate analysis performed, due to a variety of underlying factors. To my knowledge, there is no command through which STATA can perform power calculations on Spearmanʼs rank correlation coefficients. Please inform me if there is a way to overcome this difficulty. Are there any commands I am not familiar with? Would programming STATA be of value? What would be the optimal approach to this issue? The need for power calculations in Spearman's rank correlation coefficients seems justified. I thank you in advance. T.S. University of Athens, Greece ___________________________________________________________ Χρησιμοποιείτε Yahoo!; Βαρεθήκατε τα ενοχλητικά μηνύματα (spam); Το Yahoo! Mail διαθέτει την καλύτερη δυνατή προστασία κατά των ενοχλητικών μηνυμάτων http://login.yahoo.com/config/mail?.intl=gr * * For searches and help try: * http://www.stata.com/support/faqs/res/findit.html * http://www.stata.com/support/statalist/faq * http://www.ats.ucla.edu/stat/stata/ * * For searches and help try: * http://www.stata.com/support/faqs/res/findit.html * http://www.stata.com/support/statalist/faq * http://www.ats.ucla.edu/stat/stata/

**References**:**st: Spearman's rank correlation coefficient - power calculation***From:*Theo Serge <stata_theo@yahoo.gr>

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