310 PART 6 Analyzing Survival Data

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» ^{Eight participants were alive at the start of Year 2, and zero were censored}

during Year 2. So all eight participants continued to be at risk during Year 2.»

» ^{Calculations continue in the same way for the remaining years.}

Column F

Column F shows the Probability of Dying during each interval, assuming the partic-

ipant has survived up to the start of that interval. To calculate this, divide the Died

column by the At Risk column. This represents the fraction of those who were at

risk of dying at the beginning of the interval who actually died during the interval.

Formula for Column F: F = C/E.

Here’s how this formula works in Figure 22-3:»

» ^{For Year 1, the probability of dying is calculated by dividing the one death by}

the 9.5 participants at risk: 1/9.5, or 0.105 (10.5 percent).»

» ^{Zero participants died in Year 2. So, for participants surviving Year 1 and alive}

at the beginning of Year 2, the probability of dying during Year 2 is 0. Woo-hoo!»

» ^{Calculations continue in the same way for the remaining years.}

Column G

Column G shows the Probability of Surviving during each interval for participants

who have survived up to the start of that interval. Since surviving means not

dying, the equation for this column is 1 – Probability of Dying, as indicated by the

formula for Column G: G = 1 – F.

Here’s how this formula works out in Figure 22-3:»

» ^{The probability of dying in Year 1 is 0.105, so the probability of surviving in}

Year 1 is 1 – 0.105, or 0.895.»

» ^{The probability of dying in Year 2 is 0.000, so the probability of surviving in}

Year 2 is 1 – 0.000, or 1.000.»

» ^{Calculations continue in the same way for the remaining years.}

Column H

Column H shows the cumulative probability of surviving from the time of surgery

all the way through the end of this time slice. To survive from the start time

through the end of any given year (year N), the participant must survive each of