I'm reading some of the educational material for a new therapy that can help treat PPMS (Primary Progressive Multiple Sclerosis).
I'm having difficulty understanding their use of statistics.
Let's first talk in general terms:
If person A has 100 oranges, and person B has 75 oranges, then person B has 25% fewer oranges than person A.
We compute this as:
(100-75)/100 = 0.25 = 25%
Now let's get to the educational material. It states:
Overall, the percent of people with 12-week CDP was 32.9% of Ocrevus-treated people vs. 39.3% of placebo-treated people. Another way of looking at this data is to say that people treated with Ocrevus were 24% less likely to have disability progression than those treated with placebo.
I don't get it. Using the same formula as above,
(39.3-32.9)/39.3 = .163 = 16%
Yet the educational material uses a figure of 24%, not 16%.
How do they obtain that figure, and is it a common (fair, straightforward) or uncommon (misleading) way to represent that data?
(Please note that I am in no way suggesting anything is fair or misleading. I am only stating that I don't understand and am confused by what I have read.)