PREFIX person:     <tag:heathers.globalcode.info,2020:person:>
PREFIX predicate:  <tag:heathers.globalcode.info,2020:predicate:>
PREFIX thing:      <tag:heathers.globalcode.info,2020:thing:>

SELECT
	?group_name
	(count(*) AS ?member_count)
WHERE {
	?person predicate:is-member-of ?group .
	?group predicate:has-title ?group_name .
}
GROUP BY ?group_name
ORDER BY DESC(?member_count)