Great point. It depends greatly by each individual department. But I think it can be a useful metric for getting a sense on the state of the field.
It is also worth noting that this data is several years old and is self-reported. But in general, job prospects don't look favorable if more than half of biology graduate students still intend on pursuing academia.
Also, I'm a bit shock of the 37% dropout rate. Isn't that a bit high or is this rate on par with other fields?