The three best indicators of a country's level of development are: per capita GDP, literacy rate, and life expectancy. The most important indicator of a country's level of development would be per capita GDP. In the following I will discuss their indicators and give a country as an example.
Per capita GDP is the average yearly income for each person in their particular country. A country's level of development means how people make a living and, their income level. Switzerland has the worlds highest per capita GDP. It is the most important demographic because, it reflects the people's wealth and consumption capability. The more people buy and spend the higher their quality of life is.
Literacy rate is the percentage of persons aged 15 and over who can read and write a short, simple statement in their everyday life. Israel is the country with the highest literacy rate. To have a high literacy rate a country must have an organized, well-founded school system. In order to achieve this a country must have a high level of development.
Life expectancy is the average number of years that a person can be expected to live. For example, the United States life expectancy rate is 76.9 years of age. For a long life expectancy rate in a country, it would have to have high wealth, and a good medical health system.
Per capita GDP, literacy rate, and life expectancy are all demographics that can indicate a country's level of development. I consider per capita GDP the most important, but all three are necessary to achieve a high level of development.