Field note · January 6, 2024

mrr_usd by region: a 21% spread

Real group means for one column across 4 segments, and what the pooled average conceals.

1 min read ·Analytics practice ·statistics practice

Breaking mrr_usd down by region on saas-subscriptions, because the headline average is 447 and no segment is actually there.

  • LATAM — mean 501, median 99 (167 rows)
  • EMEA — mean 486, median 102 (744 rows)
  • AMER — mean 426, median 84 (1,162 rows)
  • APAC — mean 412, median 78 (427 rows)

Top to bottom that is 501 against 412, a spread of 21.5%. The pooled average is 447.

sql
select region,
  count(*)                                             as rows,
  round(avg(mrr_usd)::numeric, 2)                      as mean,
  percentile_cont(0.5) within group (order by mrr_usd) as median
from saas_subscriptions
group by 1
order by mean desc;

The groups are close enough that the pooled average is a fair summary. That is worth confirming rather than assuming: the check costs one query and the failure mode is invisible.

Notice the mean and median columns disagree most in LATAM, where the mean sits well above the median. Always compute both in the group-by. The comparison between them per segment is free and tells you whether you are looking at a level difference or a tail difference.

This is the setup for Simpson's paradox — the case where every segment moves one way and the total moves the other.