This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Statistical Tests, Subject name: Social & Preventive Medicine
Which test is used to compare kapian-meier survival curve- 
Select and explain. 
A. T-test, B. Chi-square test, C. Log rank test, D. Whitneys test
C: Log rank test
Answer: C: Log rank test 
Explanation: Ans. is 'C' i.e., Log rank test o The Kaplan-Meier estimator is an estimater for estimating the survival function from life time data. o A plot of the Kaplan-Meier estimate of the survival function is a series of horizontal steps of declining magnitude which, wrhen a large enough sample is taken, approaches the true survial function of that population. The value of the survival function between successive distinct sampled observations is assumed to be constant, o Different Kaplan-Meier curves can be compared by - The log rank test The cox proportional hazards test