Esperanto in Scotland, Chapter 6, Exercise 2
Sample answer.

You would need to know:
- how many people of each sex had listed jobs (the figures cover only those whose jobs
  were listed);
- whether women and men of the same social class were being compared;
- how "professional" was defined (teachers, nurses and stenographers were counted
  differently from, say, accountants);
- how the 1911 Antwerp Scots compare with Scots who did not travel, and with the wider
  population (the travellers were people with money and time).

Without these, the figures describe who went to Antwerp, not whether Esperanto was equal.