The methodology in the original Centurio post strikes me as essentially solid:
Using available statistical data from the center for applied research in the apostolate (1) and from various sources on the traditional institutes of priests (2), I have put together forecasts on the future number of priests until the year 2050. In order to put these forecasts together I used the simple iterative formulaFrance is an interesting case on which to do a follow-up to this analysis because although a historically Catholic country is has seen a huge reduction in church attendance and in the number of priests in recent years. France currently has 14,000 priests, with an average age of 75 and in recent years has ordained around 100 priests a year.
n (t+1) = n (t) * (1 - r) + o
where n(t+1) is the number of priests in the next year, n(t) is the number of priests in the current year, r is the rate of retirement or priests per year expressed in percent of all priests, and o is the number of ordinations of new priests each year. I was able to obtain the total number of priests as well as the number of ordinations from the sources mentioned above and input into the formula. For the retirement rate I assumed 2.5% which equals to 40 active years for a priest this means that every year 1/40 of all priests becomes inactive. I did all calculations for the individual orders of traditional priests, then summed them up to all traditional priests. I also did the calculation for all priests (currently 414,313) according to the CARA data (1).
The approach that Centurio takes is to assume that because the average age of French priests is 75, 20% of them will retire every year, while adding assuming that the most recent national ordination number (96) remains constant from here on out. With these assumptions, the number of priests stabilizes at around 480 around 2050. Given the current number of priests in traditionalist orders in France, and their growth rate, they would become the majority of French priests around 2038 with these assumptions.
The problem with this approach is that it assumes that even the new priests (being ordained at an assumed rate of 96 per year) are also retiring at a rate of 20% per year. While it may be that some French vocations are older, I think we can assume that their average age is not 75! What would be a lot more reasonable is to assume a standard length of active life for priests such as 35 years and assume that given a constant rate of ordinations the population of priests will eventually stabilize at that number times the number of ordinations. With 96 vocations per year, that would indicate a eventual priest population of 3360. Obviously, this is a much, much smaller number of priests that the current 14,000. However, it's also significantly more than the reasonably projected number of traditionalist priests. Rather than being the majority in 2050, if current trends continue traditionalist priests will make up about 16% of French priests. (This doesn't include the rate at which France imports priests from Africa and Eastern Europe.)
Even so, the decline in the number of priests is absolutely huge and says a lot about the decline in French Catholicism. This piece describes the decline in the number of seminarians:
As was the case last year, there has been a 3% drop in candidates to the priesthood (from 732 on 15 November 2010 to 710 on 15 November 2011).The come into perspective a bit, however, if you look at the percentage of the French who are actually going to mass every a week. That too has declined dramatically over time:
In order to evaluate these data over a longer period, let us recall that enrollment in French seminaries had been 4,536 at the end of the Council in 1966; it was 1,297 in 1975 during the explosive years of the liturgical reform; 1,103 in 1996 during the John Paul II years; 784 in 2005 when Benedict XVI was elected, and 710 today. There is therefore an observable 85% drop since Vatican II and nothing seems to able to stop it . . . at least so long as the outlook at the parish level remains unfavorable to the renewal of the priesthood. ... This represents the lowest level on record since the French Revolution in 1789.
A poll by IFOP for Catholic daily La Croix published in early 2010 presented data on Catholics in France. In 1965, 81% of the French declared themselves as Catholics; no more than 64% did in 2009. The decrease in active Catholics was proportionately much larger: in 1952, 27% of the French went to Mass once a week or more, while in 2006, no more than 4.5% did.
If we take the percentage of French who were weekly mass goers right before the council as 27%, and the current percent as 4.5%, we get a decline in the number of church attendees from 16 million to 3 million. This 77% decline in the absolute number of church attendees, even as the French population increased by 41%, represents a near implosion of religious practice. If you look at the number of seminarians as a function of the number of regular mass goers (after all, I think we can assume that only people who go to mass at least weekly enter the seminary) it turns out that the ratio of seminarians to mass goers hasn't changed as dramatically. In 1966 there were 3.6 seminarians per 10,000 weekly mass goers, while now there are 2.4 seminarian per 10,000 weekly mass goers -- a 33% decline. If we could control the number of mass goers for age, we might well see a flat rate.
None of this says that vocations are healthy in France, but it underscores the fact that the vocations crisis is a part of a long term decline in faith and practice by which France has pretty much ceased to be something you can call a Catholic country.