180 patients were treated for disease X from 1991 to 1993, and their progress was followed to 1994.The treatment results are above.No patients were lost to follow-up.

What is the probability of surviving for 3 years?

What impact woulda change in the effectiveness of the treatment have on analysis?

Chart used: year of treatment # of patients treated. # alive at first anniversary #alive at 2nd # alive at 3

1991 75 60 56. 48

1992 63 55 31 -

1993 42 37 - -

Totals: 180 152 87 48