If you observe a sudden population drop in a year, what should you check to identify possible causes?

• A. Only births and deaths.
• B. Migration patterns alone.
• C. Births, deaths, and migration.
• D. Weather patterns.

Answer: (C)

A population change in a single year is driven by three things: births, deaths, and migration. If you see a sudden drop, the cause could be more deaths than births or a net outflow of people, or a combination of both. To identify what happened, you need to examine all three components: how many births occurred, how many people died, and the net migration (immigration minus emigration). The basic relationship is: end population = start population + births − deaths + net migration. If births and deaths don’t show a large difference, a negative net migration could explain the decline; if deaths spike or births fall, those could be the driver.

Focusing only on births and deaths misses the impact of people moving in or out. Looking at migration alone doesn’t account for natural increase or decrease from births and deaths. Weather patterns aren’t the direct components that change population year to year, even though they can influence mortality or migration indirectly.

So, check births, deaths, and migration to identify possible causes.