Yup: Too little data. What method was employed to measure these values?
At what frequencies?

If I remember correctly, there was a frequency/attenuation chart on the
back of some foam earplugs carton I saw once in a drug store. I'm sure
ANR manufacturers have plenty of charts for their products. So, data is
obtainable, at least theoretically. But that doesn't mean much, since
noise perception is a very psychological thing (think of all those crazy
psycho-acoustic models for Hi-Fi audio noise reduction), and you cannot
really go by "more decibels = better noise cancelling" principle all the time.

Unfortunately, I cannot make comparisons myself, as I don't currently
own an ANR set. I tried passive vs. passive+foam, and the difference was
drastic. But I can't really tell how much I'm losing due to lack of selectivity
of ANR without trying one. Thus the question.



Andrey