NorthWest Biotherapeutics Inc (NWBO)

[wavelengthy]

13% comes from Kaplan Meier calculations.

It’s conditional probability that gets calculated from the first interval all the way through to the 5yr point.

not as simple as taking the number at risk at 5 years Divided by 232. You take the chance of surviving 4 years and multiply it by the probability of making it to five years if you already made it 4 years.


Looking at the treatment arm KM curve, I see 4 downward movements of the line between yr 4 and 5. Since the number at risk changes from 35 to 25 during this period, we can say 4 died and 6 were LTFU during. Under KN calculations, LTFU Numbers are normalized over that period to get the average number at risk during that period. This is often done By dividing the # LTFU in half. So the average number at risk in that period is 35 minus half of 6, which is 35 - 3 = 32. So with 4 deaths, we get 32 - 4 = 28 alive of 32 adjusted at risk. 28 / 32 = .875.

The final answer is .875 * the 4 yr survival estimate which is 15.7%. Of course this 15.7% is calculated in a similar way based on the 3 year survival probability, but i’ll take it as a given for this example.

So finally we have .875 x .157 = 13.7%

Obviously my calculation is slightly off (perhaps my LTFU adjustments or assumptions are off) since JAMA reports 13.0, but that’s the general idea.