I am using phreg to analyze the my data. However, the control frequency of the last group among the four groups is '0'. However, the hazard ratio is calculated in the phreg I do not know why the hazard ratio is calculated for any reason.
I try to write a paper using this result. I do not know what to do.
Your last group still has 4 cases... Its frequency is not zero but rounded to 0 by excel
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