The 2009 tax law included the Making Work Pay tax credit, which is a refundable tax credit equal to the lesser of 6.2 percent of a person’s earned income or $400 ($800 for married couples). The credit phases out between

$75,000 and $95,000 of adjusted gross income

($150,000 and $190,000 for married couples).

How does this tax credit influence effective marginal tax rates in the phaseout range?