The Inter-Parliamentary Union has released its Women in Parliament in 2021: The Year in Review report, a systematic count of the share of women in national legislatures around the world.

Women have been increasing their share of members in national legislatures and parliaments over time. Here’s the overview from 1995 up through 2021.

When it comes to chairing a legislative committee, women hold 27% of the seats–similar to their overall representation. However, the distribution of these chairs across types of committees is skewed.

Much of the report is a country-by-country overview of changes in the last year or or two. But overall, what causes some countries to have substantially higher shares of women than others? Cultural and historical factors surely play a role, but the report emphasizes some institutional factors as well. For example, a number of countries have a quota requirement: for example, requiring that each party must have a certain proportion of women among its legislative candidates.

As in previous years, quotas appeared to be the most critical factor in determining women’s representation in 2021. Among the 30 countries that had some form of quota system in place for the single or lower house, 31.9 per cent women were elected. This varied a little based on the type of quota – countries with legislated quotas elected 31.8 per cent women on average, and those with only voluntary quotas adopted by political parties elected 32 per cent women. On the other hand, only 19.5 per cent women were elected in lower or single houses in countries with no form of legislated or voluntary quotas.

Another institutional factor that seems to matter here is that countries where elections are by majority vote in a district seem to have a smaller share of women legislators than those with proportional voting–that is, where voters cast their ballot for a party, parties receive seats in the legislature according to how many seats they receive, and parties (mostly) determine who will fill those seats.

This report makes no effort to look at differences in how men and women vote when in legislatures. But the underlying facts seem worth noting.