Sparked by a recent conversation with , JRDA ...
We collected estimates of each league in Scotland's membership structure, by voluntary submissions to a form distributed in our community group. Of the leagues in Scotland that we believe to still be active, only 2 did not volunteer information, and 1 volunteered partial information (which was explicitly allowed in the form). We asked for the total size of the league (all members), how many of these were skaters, how many of those skaters were "rosterable" [mins-passed and able to skate], how many members officated [including double-counting skaters who also officiate], how many of those officials refereed, and, finally, how many members they had who were active in roles other than skating or officiating.
In general, the majority of leagues in Scotland fall within a broad size range of between 30 and 60 members, although there are outliers at both ends of the scale. The mean membership is 41, and the median is 32; the noticeable skew is due to the long tail at the high-end of membership. The total number of people involved in Roller Derby as part of a league (including only leagues who volunteered data) is 618. We would estimate that including the missing leagues would increase this to around 700 in total. (The number of people involved in Roller Derby in Scotland in total is higher than this, as some people are not members of any league.)
Consistently, about 50% of the membership are rosterable mins-passed skaters; the mean fraction of skaters who are rosterable is two-thirds of the total skaters, so around 80% of the membership of the "mean" Scottish league are skaters of some level. There's much less skew in these values than there are in other statistics, although there are still outliers. Almost all Scottish leagues report enough rosterable skaters to maintain at least 1 team roster (although not always a full 15) under WFTDA rules; 4 of them have enough to comfortably maintain rosters of 2 or more teams simultaneously (and if we allow up to 5 crossover skaters between A and B rosters, probably another 2 or 3 would be able to do so). We don't have any information about the change in these values from previous years, so it is difficult to speak about the sustainability of roller derby in roster terms in Scotland. (Note, however, that the number of leagues in Scotland has declined significantly from its high-point in 2016.)
Officials, on average, make up around 2/15ths (13%) of a league's membership. However, this number is highly variable, and to a greater extent than the skater fraction; whilst the mean number of Officials in a league is a disappointingly low 6, the median is an even lower 4. As with the membership numbers, this is skewed by a small number of leagues with very high numbers of Officials, multiples of the mean value; the median is a true reflection of the "typical" league's officiating roster. The "fraction of membership" is also skewed by large variations in the number of officials per skater: some leagues have membership fractions double that of the mean; whilst others have half the mean value.
A similar situation exists for Referees as a subset of Officials: the mean number of Referees per league is 3.4, but the median is only 2. (In this case, there are several leagues with zero Referees, as well as a small number with multiples of the mean.)
The total number of Officials in all the leagues who volunteered data, together, is 90, with 51 Referees.
Whilst this is hypothetically sufficient to maintain 7 simultaneous games (with 7 Referees each), it is extraordinarily unlikely that all 51 Referees would be available at the same time, or able to travel equally to those locations. (Scotland also has a significant number of "National" and "International" level Referees and NSOs, so we also compete with events outwith Scotland for our internal resources.) Empirically, it has been hard to guarantee officiating resources for more than 2 simultaneous events within Scotland, especially if those involve more than 1 bout each.
Perhaps surprisingly, the mean number of "Volunteers" per league is 10% of the total, although the low median fraction of 5% shows that this is, once again, subject to significant skew from outlier leagues. In fact, whilst the mean number of Volunteers is almost 4, the median is 1.5; many leagues have zero, 1 or 2 Volunteers, whilst a minority have multiples of the mean.