Project Survival Analysis: Colon Cancer

In a study of colon cancer, tumors were removed from the colon of 90 patients. Subsequently, the individuals were assigned to be treated either with a placebo or with the drug A. Time to the first recurrence of tumor in months is saved under variable name time in the data set ex_colon.sav (http://people.ysu.edu/~gchang/stat/Ex/ex_colon.sav). Treatment status is saved under the name group; the value 1 represents placebo. Indicators of censoring status – where 1 designates that a tumor did recur and 0 that it did not and that the observation was censored – are save under the name censor.

1) Use the product-limit method to estimate the survival function in each treatment group and construct the survival curves. 2) Does it appear that the individuals in one group have a longer time to first recurrence of tumor than those in the other group? 3) Test the null hypothesis that the distributions of recurrence times are identical in the two treatment groups. What do you conclude? 4) The variable number is an indicator of the number of tumors initially removed from the colon; 1 indicates that a patient had a single tumor, and 2 that the individual had two or more tumors. For patients treated with the placebo, test the null hypothesis that the distributions of recurrence times are identical for individuals who had one tumor and for those who had two or more tumors. What do you conclude? 5) Use the Cox regression method to study the significance of the variables number and group. Conclude your analysis with relative risk if the factor is significant.