1. Use graphs below to answer questions on survival.

1. What is the median survival time, based on Graph 1?

Graph 1. Survival following surgery (X axis: time in days).

1. What can you say about the median survival time for Group A (below)?

Graph 2. Survival function for group A.

1. What is the probability of surviving the entire follow up period?

Graph 1 _____

Graph 2 _______

1. You have calculated the survival function and plotted the K-M curve for a group of terminally ill patients following surgery. Based on the graph, what is the probability of surviving a) 1 month after surgery, b) 6 months after surgery, and c) 12 months after surgery?
2. What effect can adverse events have on main results of a clinical trial?
3. You compare serious adverse event rates in the intervention and control groups, and, while intervention group experiences a higher rate of adverse events, the result is not statistically significant (p>0.05). Does this mean the intervention is safe? What is an appropriate approach in analyzing adverse events?
4. Why is ‘intent-to-treat’ the primary analysis of main results in RCTs? (Hint: If compliance with intervention is low, is this analysis likely to overestimate or underestimate treatment effect?
5. Adherence to medication taking in your randomized trial was measured using pill count (see table below). Intent- to- treat analysis of the effect of intervention shows that treatment A is more effective than treatment B. What can you say about compliance in the trial, and the effect it could have on the results of your primary analysis? (1 paragraph)

	Treatment A (n=100)	Treatment B (n=100)
> 90%	70	50
50%-89%	15	25
20%-49%	10	20
	5	5

1. Intent- to- treat analysis shows no significant difference in outcome between intervention and control groups in a randomized clinical trial, using a simple 2x2 table. You have recorded the occurrence and time of events (outcome) and loss to follow up. You notice that 40% in each group were lost to follow up over the 3 years of trial duration. A) Discuss the potential impact of loss to follow-up on the results of your trial. B) What other analysis can you perform?
2. Results indicate lower mortality in intervention group compared to the control group in a randomized clinical trial. You notice that 40% in intervention group and 10% in the control group were lost to follow up. Discuss potential impact of loss to follow up in this trial.
3. You plan multiple interim analyses in a 5-yr trial. What procedure(s) will you use and why?

Cum Survival 1.0 .8 .6 .4 .2 0.0 Survival Function PO 0 DATE IN 2 '+ .6 '00 10 12 14