The data is from The World Happiness Report that uses survey data, demographic information and statistical analysis to rank 156 nations according to the happiness of their people.
A country’s overall happiness score is a composite of different factors including GDP per capita, healthy life expectancy and perceptions of corruption etc. The data is trying to answer what factors contributes to happiness.
Data source is at: https://www.kaggle.com/arielyeung/world-happiness-data The explanation of the data is at : https://s3.amazonaws.com/happiness-report/2019/WHR19_Ch2A_Appendix1.pdf