It is not possible to get these numbers. Each group is autonomous. Of the many groups I am familiar with none has ever tracked this type of information (over th

It is not possible to get these numbers. Each group is autonomous. Of the many groups I am familiar with none has ever tracked this type of information (over the last 30 some years). If you had 20 or so very dedicated researchers who wanted to attend the meetings of 20 different groups once a week for 5 years,it might be possible to get some good numbers.