I would like to know if censoring data is necessary to calculate the hazard ratio between 2 Kaplan Meier (KM) curves.
Censoring data is typically represented by small vertical bars atop of the curve on KM graphs.
Censoring data has an impact on the shape of a KM curve already (for instance, if 98/100 people drop from a trial, and 1 person dies, the curve goes down much more than if no one had dropped out). This makes me think that the curves are perhaps enough for calculating hazard ratios (since I understand hazard rates are akin to the slope of the curves). Is this true?
I am asking a practical question: Is having the values of survival curves over time, without the censoring information, enough to estimate the hazard ratio between these curves?
Context: I am right now digitizing KM curves. I would like to estimate the hazard ratio between them. I cannot retrieve the censoring data. Not having the censoring data is a limitation to my analysis, I know. But I would like to know: Can I nonetheless calculate the hazard ratio? Can I calculate a confidence interval for this hazard ratio?
Ideally, please let me know how the answer differs depending on whether or not we assume relative hazards between the 2 groups are constant across time.