I read an older, very different version of the book, but in this version she writes,

If I peg someone as either very compassionate or unusually cold and harsh, I already know more about them and how they are likely to behave than their age, educational background, employment, physical appearance and sex combined could ever tell me.

Earlier on the same page she wrote,

I am not alone in my belief that an individual's level of compassion is a very good predictor of how he will think and act.

So the main difference in what I remembered and what she wrote is that while I had taken away that compassion is a good predictor of behavior, it's not necessarily easy to measure, just reliable information about a person once you have measured it.