Let’s say Human Development Index indicates this “betterness” of life, and the Democracy Index indicates how democratic a country is. Then it is visible, that only democraciest democracies show a positive trend. Countries below score of 6 lose that clear correlation, because some countries managed to provide good living conditions for their citizens without being democratic. Most of them have oil.
What: Human Development Index (HDI) and Democracy Index
Where: 165 countries of the world
Source: UNDP for HDI and EIU for Democracy Index