First consider an example in which the cutoff value is high enough to include all members:
SELECT MEASURES.[%COUNT] ON 0,
TOPSUM(birthd.decade.MEMBERS, 10000, MEASURES.[%COUNT]) ON 1 FROM patients
Patient Count
1 1970s 1,520
2 1960s 1,500
3 2000s 1,433
4 1990s 1,413
5 1980s 1,400
6 1950s 1,030
7 1940s 683
8 1930s 572
9 1920s 223
10 2010s 155
11 1910s 71
SELECT MEASURES.[%COUNT] ON 0,
TOPSUM(birthd.decade.MEMBERS, 2500, MEASURES.[%COUNT]) ON 1 FROM patients
Patient Count
1970s 1,520