Field note · April 16, 2026

The overall average hides 4 different numbers

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

1 min read ·Analytics practice ·statistics practice

region splits saas-subscriptions into 4 groups. Here is what seats_now looks like inside each.

  • LATAM — mean 65, median 10 (167 rows)
  • EMEA — mean 64, median 10 (744 rows)
  • AMER — mean 56, median 8 (1,162 rows)
  • APAC — mean 54, median 8 (427 rows)

Top to bottom that is 65 against 54, a spread of 20.0%. The pooled average is 59.

sql
select region,
  count(*)                                               as rows,
  round(avg(seats_now)::numeric, 2)                      as mean,
  percentile_cont(0.5) within group (order by seats_now) 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.