I'd love to hear how you got to 8% (which sounds reasonable to me), if you can find your notes. FWIW, I think a similar "real Christian" reduction can and should be applied to Protestants and Evangelicals. We can argue later about whose reduced numbers should come out the largest :)
Self identified as Catholic 78 million
On Church Directories as Catholic 66 million
Duplications and errors in Directories avg 3%
3% is around 2 million
24% attend weekly but best metric is actually "several times a month or more" 36% as opposed to 24%, 23 million.
Looking at consistent donation v regular attendance 40-45% depending on G'town or USCCB numbers - 9 million.
Eliminate church employees in charities and social services except for religious .6, use 1
Reduce by number under 16
Reduce by estmates of CINO services - 1.2
7 +/- mil equal TC group norm in the 50s
social .5 or 1.5?
NC social 14% - 6 mil? % of 78 or 66 =================================
I remember I used studies done by Georgetown, ND, USCCB, the Vatican, and a study done in the fifties by a group of dioceses in the NE?. Maybe not the NE but a regional group of large dioceses. I also remember a study by a university or group in San Diego that I used but don't remember the specifics, it focused on when parents stopped making kids go and so on.
I'll see if I can get all those links but I thought this might be a start for you. My thought was to measure what number of folks now are equal to the norm in the fifties and that may or may not be a good benchmark. Seemed like a good idea at the time, as they say.