The GDP per capita in Tonga is $4,600 while in Yemen it is $2,500

This entry shows GDP on a purchasing power parity basis divided by population as of 1 July for the same year. A nation's GDP at purchasing power parity (PPP) exchange rates is the sum value of all goods and services produced in the country valued at prices prevailing in the United States. This is the measure most economists prefer when looking at per-capita welfare and when comparing living conditions or use of resources across countries. The measure is difficult to compute, as a US dollar value has to be assigned to all goods and services in the country regardless of whether these goods and services have a direct equivalent in the United States (for example, the value of an ox-cart or non-US military equipment); as a result, PPP estimates for some countries are based on a small and sometimes different set of goods and services. In addition, many countries do not formally participate in the World Bank's PPP project that calculates these measures, so the resulting GDP estimates for these countries may lack precision. For many developing countries, PPP-based GDP measures are multiples of the official exchange rate (OER) measure. The differences between the OER- and PPP-denominated GDP values for most of the wealthy industrialized countries are generally much smaller.
Source: CIA World Factbook

The number of deaths of infants under one year old in a given year per 1,000 live births in Tonga is 11.28 while in Yemen it is 56.77.

This entry gives the number of deaths of infants under one year old in a given year per 1,000 live births in the same year; included is the total death rate, and deaths by sex, male and female. This rate is often used as an indicator of the level of health in a country.
Source: CIA World Factbook

Tonga has an unemployment rate of 13.00% while Yemen has 35.00%

This entry contains the percent of the labor force that is without jobs.
Source: CIA World Factbook

The life expectancy at birth in Tonga is 71.03 while in Yemen it is 63.36.

This entry contains the average number of years to be lived by a group of people born in the same year, if mortality at each age remains constant in the future. The entry includes total population as well as the male and female components. Life expectancy at birth is also a measure of overall quality of life in a country and summarizes the mortality at all ages. It can also be thought of as indicating the potential return on investment in human capital and is necessary for the calculation of various actuarial measures.
Source: CIA World Factbook