Call:
lm(formula = y ~ x)

Residuals:
     Min       1Q   Median       3Q      Max 
-0.07591 -0.04519 -0.00388 -0.00384  0.64917 

Coefficients:
                     Estimate Std. Error t value     Pr(>|t|)    
(Intercept)          0.003879   0.004484   0.865        0.387    
xLow income          0.014234   0.010094   1.410        0.159    
xLower middle income 0.046228   0.008116   5.696 0.0000000180 ***
xNA                  0.072032   0.015464   4.658 0.0000038160 ***
xUpper middle income 0.041575   0.007496   5.547 0.0000000412 ***
---
Signif. codes:  0 ‘***’ 0.001 ‘**’ 0.01 ‘*’ 0.05 ‘.’ 0.1 ‘ ’ 1

Residual standard error: 0.07831 on 707 degrees of freedom
Multiple R-squared:  0.07772,	Adjusted R-squared:  0.0725 
F-statistic: 14.89 on 4 and 707 DF,  p-value: 0.00000000001082