From the table above, we can see that for last 100 years from 1900 until 2000, Belgium have the highest population for people aged 65 and over in the three countries (Australia, Belgium, and Costa Rica). Belgium have the biggest portion for that population with an average up to 50% from total in the three countries each year. Contrast from Belgium, Costa Rica have the lowest population for that aged each year of observation. This data need more research to check what is behind the situation. We must compare based on total population from each country and check the composition for the population aged below 65. After we get all the data, we can analyze and compare them to make sure fair condition on observation. The conclusion, can lead us to other assumptions to check, like birth rate, death rate, etc. Maybe that Belgium have highest birth rate or maybe Costa Rica have highest death rate, and many others assumption and conclusion we can get.