Call:
lm(formula = y ~ x)

Residuals:
     Min       1Q   Median       3Q      Max 
-0.15075 -0.00243 -0.00071 -0.00068  0.39779 

Coefficients:
                       Estimate Std. Error t value             Pr(>|t|)    
(Intercept)           0.0007090  0.0038218   0.186                0.853    
xLow income           0.1500403  0.0086025  17.441 < 0.0000000000000002 ***
xLower middle income  0.0301101  0.0069174   4.353            0.0000154 ***
xNA                  -0.0005116  0.0131798  -0.039                0.969    
xUpper middle income  0.0017227  0.0063883   0.270                0.787    
---
Signif. codes:  0 ‘***’ 0.001 ‘**’ 0.01 ‘*’ 0.05 ‘.’ 0.1 ‘ ’ 1

Residual standard error: 0.06674 on 707 degrees of freedom
Multiple R-squared:  0.3182,	Adjusted R-squared:  0.3144 
F-statistic:  82.5 on 4 and 707 DF,  p-value: < 0.00000000000000022