title: How to combine hazard ratios and confidence intervals from Cox regression analyses in R
body: <p>I have performed a Cox regression analysis including four variables (sex, age and two binary explanatory variables) which all have significant associations to outcome. I have used the coxph function from the "survival" package in R:</p>
  
  <pre><code>    library(survival)
  cox &lt;- coxph(Surv(time, status_risk==1) ~ sex + age + stone_number +stone_size, data=cox_cut)
      summary(cox1_3_cut)
  Call:
  coxph(formula = Surv(time, status_risk == 1) ~ sex + age + 
  stone_number + stone_size, data = cox_cut)
  
  n= 582, number of events= 48 
  (82 observations deleted due to missingness)
  
                        coef exp(coef) se(coef)      z Pr(&gt;|z|)    
  sexfemale              0.76993   2.15961  0.34577  2.227 0.025966 *  
  age                   -0.03222   0.96829  0.01201 -2.682 0.007311 ** 
  stone_number&gt;=2        0.60646   1.83393  0.29942  2.025 0.042821 *  
  stone_size&gt;10          1.02593   2.78969  0.29391  3.491 0.000482 ***
  ---
  Signif. codes:  0 ‘***’ 0.001 ‘**’ 0.01 ‘*’ 0.05 ‘.’ 0.1 ‘ ’ 1
  
                    exp(coef) exp(-coef) lower .95 upper .95
  sexfemale                2.1596     0.4630    1.0966    4.2530
  age                      0.9683     1.0327    0.9458    0.9914
  stone_number&gt;=2          1.8339     0.5453    1.0198    3.2980
  stone_size&gt;10            2.7897     0.3585    1.5681    4.9629
  </code></pre>
  
  <p>I would like to make a prediction score table including the four variables with 4 age stratified Groups (30, 40, 50, 60 years of age). All hazards in this table must be divided by one predefined hazard in order to obtain HR for each age group.    </p>
  
  <p>How to compute the HR with the 95% CI for each of these specific age-groups in R?</p>