I have run some of the same analyses on the Diocese of Washington, and have come up with some quite surprising results: although some of the aggregate numbers are similar, the details are almost entirely different.
Let's start with some geography, and then some history. The diocese of Washington was carved out of the Diocese of Maryland because what at its peak was over two hundred parishes (and probably close to it, back in the day) is way too much for one bishop to administer. (Easton, the eastern shore portion, was split off much sooner, I would guess due to travel issues during the Civil War.) Back then, both dioceses had an urban core surrounded by a great sea of rural space, but this similarity was deceptive, and the evolution of both the city and especially the suburbs would lead to very different social contexts for the two.
Washington, now, consists of a central mass of urban density wrapped by a blanket of outer suburbs that fades to nothing on the south side, and bracketed by two very different rural areas. The Western end is like Diocese of Maryland territory, with a mixture of farm and outer suburbs and a sprinkling of late Vicky carpenter gothic town churches. The southern one contains the oldest settlements in the state and is served by scattered chapels of ease, mostly Georgian in style. The diocese also contains the black heartland of the state. Maryland by contrast has a large rural western area which is isolated, very white, and Appalachian more than farm rural, and the built-up urban area is much smaller, but also poorer. Howard (in the diocese of Maryland) and Montgomery (in Washington) are at the top of the income pyramid in the entire country, but Montgomery is much larger, and over a third of it is essentially city, whereas Howard has no truly urban area at all (Columbia being, when all is said and done, an experiment in making a really large subdivision). Economically, DC and its suburbs have waxed and waxed, while Baltimore has waned.
In the orthodoxy wars, the two dioceses were both focal points, but with very different issues, policies, and outcomes. The big story in DC, of course, was the fight over imposing Jane Dixon on several conservative parishes; the diocese won, in the end, and I don't know of any parishes which left all or in part. Maryland, on the other hand, was a focus of resistance, as symbolized in the Baltimore Declaration, but also as realized in the departure of two parishes and the riving of St. Peter's Ellicott City, which has suffered through other crises since and is only now, perhaps, showing signs of recovery.
And then, of course, there is the National Cathedral, which shows something else about DC: it has big destination parishes.
So, enough prelude, and on to the music. Washington also shows ASA loss through the decade, but not to the same degree: 23% to Maryland's 27%. It lost fewer parishes as well, three to Maryland's ten, though in the latter case there were actually twelve losses and two missions started. I don't have information on whether any of the Washington parishes started in this time frame, but there's nothing to suggest that any did. Now, the cathedral, in 2005, accounted for more than 10% of diocesan ASA, so when it is excluded, the two dioceses have close to comparable attendance, with Washington running about 2,000 larger at both ends of the decade. But the cathedral's attendance tanked starting in 2012, which perhaps not coincidentally is when Gary Hall arrived as dean, so that attendance in 2015 was about two-thirds that in 2005. The rest of the parishes declined, in the aggregate, 21%.
In the midst of this, another number stands out: parishes in Washington are just bigger. I didn't go through the work needed to get specific numbers for each parish, so I cannot give a median, but the mean parish in Washington (ignoring the cathedral) had an ASA of 163 in 2005 and 135 a decade later; Maryland's average parish started smaller (113) and shrunk more, to say nothing of the closures.
Staffing is another area where there are conspicuous differences. Washington doesn't do permanent deacons, and thus I found a single deacon listed in the entire diocese. I didn't keep track of associate positions, but I did some of the same analysis for rectors and priests-in-charge that I did for Maryland, and found strikingly different patterns. Maryland, recall, has a lot of home-grown priests and many cases where the newly-ordained stepped directly into being the sole priest in a parish. Neither pattern obtains in Washington: half as many rectors in Washington were ordained in that diocese, and only five went directly from being ordained to running a parish. (One of the latter was ordained in Maryland by, yes, Eugene Sutton.) Beyond that, Washington rectors represent a wider range of dioceses, with the more conservative dioceses better represented (which is to say, at all): Two were ordained by Duncan in Pittsburgh; one from Salmon in South Carolina. But then there is not a lot of commonality between the lists for the two dioceses: the total number is about the same, but only eleven show up in both lists, and other than the two home dioceses, only Virginia has more than one in both lists, no doubt due to the bishop there accosting VTS graduates. Only five parishes were in transition (I think-- there was one person whose peregrinations greatly confused this) as compared to three times the number in Maryland.
And then there is money. I have recently come across this table which is particularly interesting, as it reports non-P&P income, such as endowments. The range in the latter is extreme: ignoring Navaholand, which gets major support from the national church, on the one end we see New York in which P&P accounts for just under half of total revenue, and at the other Upper South Carolina, where P&P accounts for 95%. Now, the cathedral again undoubtedly skews Washington numbers, considering that out of P&P of $33M, it supplies $2M; I have no idea how much it skews endowment income but the contribution must be substantial. Nonetheless, again, in nearly every way Washington is more prosperous than Maryland: people give more, the pledges are larger, and the non-P&P income is larger; and all of this is spread across fewer parishes with more attendees. The only place were Maryland comes out ahead is in the plate, where the average attendee gives $371 a year versus $319 in Washington. One is tempted to assume this reflects the basic prosperity of the two regions.