title: survdiff one-sample test - how can I use the offset term in a formula?
body: <p>I would like to use the survdiff function for a one-sample test.</p>
  
  <p>I did not understand where should I include in the furmula the offset term. </p>
  
  <p>The <code>surdiff</code> should look like this:</p>
  
  <pre><code>survdiff(formula, data, subset, na.action, rho=0)
  </code></pre>
  
  <p>For ex., in k-samples test, the formula would be: <code>Surv(futime, fustat)</code> and the predictors is: <code>rx</code>. And we would use the surdiff in the following way:</p>
  
  <pre><code>survdiff(Surv(futime, fustat) ~ rx,data=ovarian) 
  </code></pre>
  
  <p>(This ex. is taken from the R example)</p>
  
  <p>What I do not understand is, how I should include the offset term in the predictors in a case I want to perform a one-sample test. In the R explanation they say I should use the offset(sp) where sp is the probabilities vector.</p>
  
  <p>Does anyone can tell me what is the correct syntax for this, and do they mean by 'include'?</p>
  
  <p>Thanks in advance!!
  Alley</p>