How to interpret migration statistics

Short answer: before using a number about migration, find out what it counts (people who arrived, who live in the country or who sought asylum), what period it covers, who produced it and how it was measured. Compare numbers of the same type and use proportions, not just totals. Migration statistics are sensitive to definitions, so comparisons call for care.

What helps before you start

• The number or chart you want to understand, with its source.
• Access to an official source or an international statistical body.
• Attention to news and posts that use numbers to support political positions.

Steps

1. Find out what is being counted. "Migrants" can mean people born abroad, people with another nationality, people who arrived in a given period, asylum seekers or people in irregular status. These are different groups.
2. Distinguish flow from stock. Flow is how many people arrive in a period; stock is how many live in a place at a given time.
3. Check the period and date. Migration data change quickly and sources may lag by years.
4. Check the source and method. Censuses, administrative records, sample surveys and estimates have advantages and limits.
5. Look for the margin of uncertainty. Estimates of irregular migration, in particular, are approximate.
6. Use proportions when comparing. A large absolute number can be small relative to a country's population, and the reverse is also true.
7. Compare what is comparable. Countries define migrants in different ways.
8. Observe the context. Crises, changes in law and specific events can explain variations.
9. Be suspicious of charts that cut axes or use misleading scales.

An example

Two news stories spoke of an "increase in migrants" in a country. The first cited the total of foreign-born people; the second, the number of asylum applications in a year. Both numbers were correct, but described different things. Spotting this, Marina understood that the stories did not contradict each other. This is an illustrative example.

Common mistakes

• Mixing categories: migrant, refugee, asylum seeker and irregular immigrant are not synonyms.
• Comparing numbers from different periods or countries without adjustment.
• Ignoring the margin of error.
• Using a single number to support a strong conclusion.
• Forgetting that each number represents people, not just statistics.

Next step

Next time you read a number about migration, answer: what is being counted, from when and who produced it. Only then compare and conclude.