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Re: st: interaction terms in a Cox model

From   Steven Samuels <>
Subject   Re: st: interaction terms in a Cox model
Date   Sat, 14 Apr 2007 22:56:21 -0400

In general, failure to reject the null hypothesis does not mean that it is true. Tests for interactions notoriously have low power. If there is one strong interaction (one age category, say) it will be masked and an omnibus test could be insignificant. That said, the size of the z statistics in your case indicates that the interactions are weak at best. You should, however, look at the full two-way table of HR's (age group x gender) to satisfy yourself that this is the case. That is create a 6 category age-gender combination variable ( "egen age_gender= group(agecat gender) will do this.,


On Apr 14, 2007, at 9:06 PM, Ashwin Ananthakrishnan wrote:


Since the P >0.05 for the null hypothesis that the
interaction terms are equal to zero, is it safe to
conclude that there is no significant interaction
between race and gender?

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