You want to investigate the effect of GDP per capita (measured in thousands of dollars) on Life
Expectancy (measured in years) and you decide to use a quadratic model. You estimate using data for
a large number of countries and obtain the following results:
Life Expectancy = 62 + 21,600GDP$_{pc}$ - 180GDP$_{pc}^2$
According to your estimated relationship, the marginal effect of GDP per capita on Life Expectancy
is positive (positive/negative/constant) up to a GDP per capita of
thousands of dollars (use an integer number in your answer), after which it becomes
(positive/negative/constant).
Note: in the first and last blank, choose only one of the options and make sure to use the correct
spelling.